Systems and methods for fuel system pressure sensor rationalization

ABSTRACT

Methods and systems are provided for determining an offset of a pressure sensor that is used for monitoring pressure in a fuel system that is sealed expect for refueling and other diagnostic events. In one example, a method includes waking a controller of a vehicle when it is expected that a pressure in a fuel system that is sealed from atmospheric pressure is at atmospheric pressure, unsealing the fuel system, and indicating an offset of the pressure sensor based on a pressure change after the fuel system is unsealed. In this way, pressure sensor offset may be determined regularly without undesirably loading a fuel vapor storage canister with vapors, which may be particularly advantageous for hybrid vehicles.

FIELD

The present description relates generally to methods and systems fordetermining an inherent offset for a fuel tank pressure transducer.

BACKGROUND/SUMMARY

Certain hybrid electric vehicles, such as plug in hybrid vehicles(PHEVs) for example, have sealed fuel systems. The reason for a sealedfuel system is because for such vehicles, engine run time may belimited, and thus opportunities for using engine manifold vacuum topurge a fuel vapor storage canister that captures and stores fuel vaporsfrom the fuel system, may too be limited. As such vehicles may be drivenin electric only mode, if the fuel system were not sealed, diurnal andrunning loss fuel vapors may overload the fuel vapor storage canister,which may result in undesired bleed emissions to atmosphere.

Such fuel systems may be sealed via a fuel tank isolation valvepositioned in a conduit coupling a fuel tank to such a fuel vaporstorage canister. In one example, to refuel a fuel tank that isotherwise sealed, a vehicle operator may depress a switch at a dash ofthe vehicle, and a controller may command the fuel tank unsealed. Thecontroller may then monitor pressure in the fuel system, and whenpressure in the fuel system is within a threshold of atmosphericpressure, then a fuel door may be commanded unlocked to enablerefueling.

In another example, diagnostic routines may be conducted on a fuelsystem and/or evaporative emissions control systems of such vehicles, toconfirm that the systems are not degraded, or in other words, to ensurethat there are no sources of undesired evaporative emissions stemmingfrom the fuel system and/or evaporative emissions system. For example,undesired evaporative emissions detection routines may be performedwhile the engine is running using engine intake manifold vacuum. Inanother example, undesired evaporative emissions detection routines maybe performed when the vehicle is off using engine-off natural vacuum(EONV) generated due to a change in temperature and pressure within thefuel tank following engine shutdown and/or with vacuum supplemented froma vacuum pump. In some examples for sealed fuel systems, standingpressure or vacuum greater than predetermined thresholds in the fuelsystem during vehicle-off conditions may be indicative of a fuel systemthat is free from a source of undesired evaporative emissions.

Routines such as fuel tank depressurization and/or routines for checkinga presence or an absence of undesired evaporative emissions rely on afunctional fuel tank pressure transducer (FTPT) to measure the pressureor vacuum within the fuel system. As such, the rationality of the FTPTmust be periodically tested and confirmed. The FTPT may be tested foroffset, to determine if a baseline output of the FTPT is accurate. Forexample, if there is an inherent offset for the FTPT, then in some casesthe fuel door may not open in response to a request to refuel, which maybe frustrating and inconvenient to a vehicle operator or customer. Inother examples, an inherent offset of the FTPT may lead to adetermination that the fuel system is free from a presence of undesiredevaporative emissions, when in fact it is not.

One example approach for an FTPT offset test is shown by Jentz et al. inUS 2015/0075251. Therein, the fuel tank is vented to atmosphere for alengthy vehicle-off soak. If the FTPT is functional, a value within athreshold of atmospheric pressure should be output following thevehicle-off soak. A deviation from atmospheric pressure may result in adiagnostic trouble code (DTC) being set at the controller, and/or mayresult in the FTPT output being adjusted to compensate for any offset.

However, the inventors herein have recognized potential issues with suchsystems. As discussed above, venting the fuel tank to atmosphere mayresult in fuel vapor trafficking to the fuel vapor canister, which maybe undesirable for vehicles with limited engine run-time asopportunities for purging the fuel vapor canister to engine intake maybe limited. If the engine must be forced on to purge the canister, thefuel efficiency of the vehicle may be reduced.

Furthermore, such an approach may not be possible for autonomousvehicles or other vehicles that participate in car-sharing models.Discussed herein, a car-sharing model includes a model of car rentalwhere people rent vehicles for short periods of time. In some examples,a customer may pay for the use of such a vehicle by the hour, as afunction of miles driven, etc. Such vehicles may accumulate much moremileage in a short period of time than vehicles that do not participatein car-sharing. Accordingly, long vehicle-off soak times may notregularly occur for such vehicles in which to determine FTPT offset.

In another example, U.S. Pat. No. 8,353,273 teaches coupling a fuel tankto a pump in order to generate a pressure signal in the fuel tank and atthe position of the pump, and correlating fuel tank pressure with thepressure indicated at the pump. A fault signal may be generatedresponsive to the correlating.

However, the inventors herein have recognized potential issues with sucha system. As one example, coupling the fuel tank to the pump may resultin fuel vapors from the tank being routed to the fuel vapor canister,which is undesirable in vehicles with limited engine run-time, asdiscussed above. Furthermore, the use of an onboard pump adds costs andcomplexity to the engine system, and not all current and future vehiclesare being designed with such a pump. A diagnostic that does notpotentially load the canister and does not include the use of a pump isdesirable.

In one example, the issues described above may be addressed by a methodcomprising waking a controller of a vehicle when it is expected that apressure in a fuel system that is sealed from atmosphere is atatmospheric pressure, unsealing the fuel system, and indicating anoffset of a pressure sensor used to monitor the pressure in the fuelsystem based on a pressure change as indicated via the pressure sensorafter the fuel system is unsealed. In this way, the offset of thepressure sensor may be indicated without increasing a potential forrelease of undesired evaporative emissions to the environment.

The above advantages and other advantages, and features of the presentdescription will be readily apparent from the following DetailedDescription when taken alone or in connection with the accompanyingdrawings.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an example vehicle propulsion system.

FIG. 2 schematically shows an example vehicle system with a fuel systemand an evaporative emissions system.

FIG. 3 depicts an example method for determining potential issuesassociated with fuel tank depressurization in response to a request torefuel a fuel tank.

FIG. 4 depicts an example lookup table with several outcomes fordiagnosing the fuel system according to the method depicted at FIG. 3.

FIG. 5A depicts an example timeline for a first outcome of the lookuptable depicted at FIG. 4.

FIG. 5B depicts an example timeline for a second outcome of the lookuptable depicted at FIG. 4.

FIG. 5C depicts an example timeline for a third outcome of the lookuptable depicted at FIG. 4.

FIG. 6 schematically shows a graphic depiction of a diurnal cycle.

FIG. 7 graphically depicts a transfer function used to convert fuelsystem pressure to a voltage for use with a comparator circuit depictedat FIG. 8.

FIG. 8 schematically shows an example comparator circuit for waking acontroller of a vehicle based on fuel system pressure.

FIG. 9 depicts an example method for determining a fuel tank pressuretransducer offset after the controller is woken via the comparatorcircuit of FIG. 8.

FIG. 10 depicts an example timeline for determining the fuel tankpressure transducer offset according to the method of FIG. 9.

DETAILED DESCRIPTION

The following description relates to systems and methods for diagnosingissues related to fuel system integrity. For example, fuel systemintegrity may relate to operational state of a fuel tank pressuretransducer (FTPT) and/or to function of one or more valves configured toseal the fuel system. In some examples, fuel system integrity may relateto restrictions in one or more lines that couple the fuel system toatmosphere. The systems and methods discussed herein may be particularlyuseful for hybrid electric vehicles with limited engine run time, suchas the hybrid vehicle depicted at FIG. 1. FIG. 2 depicts a fuel systemthat is selectively coupled to a fuel vapor storage canister and toatmosphere via a fuel tank isolation valve (FTIV). A fuel tank pressuretransducer is positioned in a line that couples the fuel system to thefuel vapor storage canister. In one example, the fuel tank pressuretransducer may be relied upon for unlocking a refueling lock (e.g. fueldoor) that provides access to a fuel filler neck for refueling a fueltank of the fuel system. Specifically, in response to a request torefuel, the FTIV may be commanded open and the refueling lock may beunlocked responsive to the FTPT indicating that the fuel system iswithin a threshold range of atmospheric pressure. However, if the fuelsystem is not depressurizing and thus not allowing access to the fuelfiller neck, then either the FTPT may be degraded (e.g. stuck in rangeor with an inherent offset), or there may be a restriction in the one ormore lines that couple the fuel system to atmosphere (e.g. FTIV stuckclosed and/or blockage in the one or more lines) that is preventingdepressurization. Accordingly, FIG. 3 depicts an example method fordetermining the source of the lack of depressurization in suchsituations. The example method depicted at FIG. 3 may rely on both fuelsystem pressure measurements and fuel level measurements duringrefueling the fuel tank, and a diagnosis may be made based on a lookuptable, such as the lookup table of FIG. 4. Such a lookup table includesthree potential outcomes, each of which are described by the timelinesof FIGS. 5A-5C.

Thus, the method of FIG. 3 relies on a refueling event, but it is hereinrecognized that for hybrid vehicles, such vehicles may go long periodsof time without refueling, and thus another method for rationalizing theFTPT is presented that relies on diurnal cycle changes, such as thediurnal cycle depicted at FIG. 6. Such a method may include waking acontroller of the vehicle at a particular time of a diurnal cycle whenit is expected that the fuel system will be at or very near atmosphericpressure. In this way, the fuel system may be unsealed and FTPT offsetdetermined, without undesirably loading the fuel vapor storage canisterwith fuel vapors, and/or without drawing in air into the fuel system.Such a method is depicted at FIG. 9, and relies on a transfer functionas depicted at FIG. 7 for latching an input voltage to a comparatorcircuit that is depicted at FIG. 8, such that the comparator circuitwakes the controller when the sealed fuel system is expected to be at ornear atmospheric pressure in order to determine FTPT offset as via themethod of FIG. 9. A timeline depicted how the method of FIG. 9 isconducted, is depicted at FIG. 10.

FIG. 1 illustrates an example vehicle propulsion system 100. Vehiclepropulsion system 100 includes a fuel burning engine 110 and a motor120. As a non-limiting example, engine 110 comprises an internalcombustion engine and motor 120 comprises an electric motor. Motor 120may be configured to utilize or consume a different energy source thanengine 110. For example, engine 110 may consume a liquid fuel (e.g.,gasoline) to produce an engine output while motor 120 may consumeelectrical energy to produce a motor output. As such, a vehicle withpropulsion system 100 may be referred to as a hybrid electric vehicle(HEV).

Vehicle propulsion system 100 may utilize a variety of differentoperational modes depending on operating conditions encountered by thevehicle propulsion system. Some of these modes may enable engine 110 tobe maintained in an off state (i.e., set to a deactivated state) wherecombustion of fuel at the engine is discontinued. For example, underselect operating conditions, motor 120 may propel the vehicle via drivewheel 130 as indicated by arrow 122 while engine 110 is deactivated.

During other operating conditions, engine 110 may be set to adeactivated state (as described above) while motor 120 may be operatedto charge energy storage device 150. For example, motor 120 may receivewheel torque from drive wheel 130 as indicated by arrow 122 where themotor may convert the kinetic energy of the vehicle to electrical energyfor storage at energy storage device 150 as indicated by arrow 124. Thisoperation may be referred to as regenerative braking of the vehicle.Thus, motor 120 can provide a generator function in some examples.However, in other examples, generator 160 may instead receive wheeltorque from drive wheel 130, where the generator may convert the kineticenergy of the vehicle to electrical energy for storage at energy storagedevice 150 as indicated by arrow 162.

During still other operating conditions, engine 110 may be operated bycombusting fuel received from fuel system 140 as indicated by arrow 142.For example, engine 110 may be operated to propel the vehicle via drivewheel 130 as indicated by arrow 112 while motor 120 is deactivated.During other operating conditions, both engine 110 and motor 120 mayeach be operated to propel the vehicle via drive wheel 130 as indicatedby arrows 112 and 122, respectively. A configuration where both theengine and the motor may selectively propel the vehicle may be referredto as a parallel type vehicle propulsion system. Note that in someexamples, motor 120 may propel the vehicle via a first set of drivewheels and engine 110 may propel the vehicle via a second set of drivewheels.

In other examples, vehicle propulsion system 100 may be configured as aseries type vehicle propulsion system, whereby the engine does notdirectly propel the drive wheels. Rather, engine 110 may be operated topower motor 120, which may in turn propel the vehicle via drive wheel130 as indicated by arrow 122. For example, during select operatingconditions, engine 110 may drive generator 160 as indicated by arrow116, which may in turn supply electrical energy to one or more of motor120 as indicated by arrow 114 or energy storage device 150 as indicatedby arrow 162. As another example, engine 110 may be operated to drivemotor 120 which may in turn provide a generator function to convert theengine output to electrical energy, where the electrical energy may bestored at energy storage device 150 for later use by the motor.

Fuel system 140 may include one or more fuel storage tanks 144 forstoring fuel on-board the vehicle. For example, fuel tank 144 may storeone or more liquid fuels, including but not limited to: gasoline,diesel, and alcohol fuels. In some examples, the fuel may be storedon-board the vehicle as a blend of two or more different fuels. Forexample, fuel tank 144 may be configured to store a blend of gasolineand ethanol (e.g., E10, E85, etc.) or a blend of gasoline and methanol(e.g., M10, M85, etc.), whereby these fuels or fuel blends may bedelivered to engine 110 as indicated by arrow 142. Still other suitablefuels or fuel blends may be supplied to engine 110, where they may becombusted at the engine to produce an engine output. The engine outputmay be utilized to propel the vehicle as indicated by arrow 112 or torecharge energy storage device 150 via motor 120 or generator 160.

In some examples, energy storage device 150 may be configured to storeelectrical energy that may be supplied to other electrical loadsresiding on-board the vehicle (other than the motor), including cabinheating and air conditioning, engine starting, headlights, cabin audioand video systems, etc. As a non-limiting example, energy storage device150 may include one or more batteries and/or capacitors.

Control system 190 may communicate with one or more of engine 110, motor120, fuel system 140, energy storage device 150, and generator 160.Control system 190 may receive sensory feedback information from one ormore of engine 110, motor 120, fuel system 140, energy storage device150, and generator 160. Further, control system 190 may send controlsignals to one or more of engine 110, motor 120, fuel system 140, energystorage device 150, and generator 160 responsive to this sensoryfeedback. Control system 190 may receive an indication of an operatorrequested output of the vehicle propulsion system from a vehicleoperator 102. For example, control system 190 may receive sensoryfeedback from pedal position sensor 194 which communicates with pedal192. Pedal 192 may refer schematically to a brake pedal and/or anaccelerator pedal. Furthermore, in some examples control system 190 maybe in communication with a remote engine start receiver 195 (ortransceiver) that receives wireless signals 106 from a key fob 104having a remote start button 105. In other examples (not shown), aremote engine start may be initiated via a cellular telephone, orsmartphone based system where a user's cellular telephone sends data toa server and the server communicates with the vehicle to start theengine.

Energy storage device 150 may periodically receive electrical energyfrom a power source 180 residing external to the vehicle (e.g., not partof the vehicle) as indicated by arrow 184. As a non-limiting example,vehicle propulsion system 100 may be configured as a plug-in hybridelectric vehicle (HEV), whereby electrical energy may be supplied toenergy storage device 150 from power source 180 via an electrical energytransmission cable 182. During a recharging operation of energy storagedevice 150 from power source 180, electrical transmission cable 182 mayelectrically couple energy storage device 150 and power source 180.While the vehicle propulsion system is operated to propel the vehicle,electrical transmission cable 182 may disconnected between power source180 and energy storage device 150. Control system 190 may identifyand/or control the amount of electrical energy stored at the energystorage device, which may be referred to as the state of charge (SOC).

In other examples, electrical transmission cable 182 may be omitted,where electrical energy may be received wirelessly at energy storagedevice 150 from power source 180. For example, energy storage device 150may receive electrical energy from power source 180 via one or more ofelectromagnetic induction, radio waves, and electromagnetic resonance.As such, it should be appreciated that any suitable approach may be usedfor recharging energy storage device 150 from a power source that doesnot comprise part of the vehicle. In this way, motor 120 may propel thevehicle by utilizing an energy source other than the fuel utilized byengine 110.

Fuel system 140 may periodically receive fuel from a fuel sourceresiding external to the vehicle. As a non-limiting example, vehiclepropulsion system 100 may be refueled by receiving fuel via a fueldispensing device 170 as indicated by arrow 172. In some examples, fueltank 144 may be configured to store the fuel received from fueldispensing device 170 until it is supplied to engine 110 for combustion.In some examples, control system 190 may receive an indication of thelevel of fuel stored at fuel tank 144 via a fuel level sensor. The levelof fuel stored at fuel tank 144 (e.g., as identified by the fuel levelsensor) may be communicated to the vehicle operator, for example, via afuel gauge or indication in a vehicle instrument panel 196.

The vehicle propulsion system 100 may also include an ambienttemperature/humidity sensor 198, and a roll stability control sensor,such as a lateral and/or longitudinal and/or yaw rate sensor(s) 199. Thevehicle instrument panel 196 may include indicator light(s) and/or atext-based display in which messages are displayed to an operator. Thevehicle instrument panel 196 may also include various input portions forreceiving an operator input, such as buttons, touch screens, voiceinput/recognition, etc. For example, the vehicle instrument panel 196may include a refueling button 197 which may be manually actuated orpressed by a vehicle operator to initiate refueling. For example, inresponse to the vehicle operator actuating refueling button 197, a fueltank in the vehicle may be depressurized so that refueling may beperformed. In some examples, a refueling lock (e.g. fuel door, etc.) maybe manually opened via a vehicle operator depressing a manual refuelinglock button 191. Such a manual refueling lock button may be positionedin a trunk of the vehicle, for example.

Control system 190 may be communicatively coupled to other vehicles orinfrastructures using appropriate communications technology, as is knownin the art. For example, control system 190 may be coupled to othervehicles or infrastructures via a wireless network 131, which maycomprise Wi-Fi, Bluetooth, a type of cellular service, a wireless datatransfer protocol, and so on. Control system 190 may broadcast (andreceive) information regarding vehicle data, vehicle diagnostics,traffic conditions, vehicle location information, vehicle operatingprocedures, etc., via vehicle-to-vehicle (V2V),vehicle-to-infrastructure-to-vehicle (V2I2V), and/orvehicle-to-infrastructure (V2I or V2X) technology. The communication andthe information exchanged between vehicles can be either direct betweenvehicles, or can be multi-hop. In some examples, longer rangecommunications (e.g. WiMax) may be used in place of, or in conjunctionwith, V2V, or V2I2V, to extend the coverage area by a few miles. Instill other examples, vehicle control system 190 may be communicativelycoupled to other vehicles or infrastructures via a wireless network 131and the internet (e.g. cloud), as is commonly known in the art. In someexamples, control system may be coupled to other vehicles orinfrastructures via wireless network 131, in order to retrieveinformation that may be applicable to route-learning, as will bediscussed in detail below.

Vehicle system 100 may also include an on-board navigation system 132(for example, a Global Positioning System) that an operator of thevehicle may interact with. The navigation system 132 may include one ormore location sensors for assisting in estimating vehicle speed, vehiclealtitude, vehicle position/location, etc. This information may be usedto infer engine operating parameters, such as local barometric pressure.As discussed above, control system 190 may further be configured toreceive information via the internet or other communication networks.Information received from the GPS may be cross-referenced to informationavailable via the internet to determine local weather conditions, localvehicle regulations, etc. In one example, information received from theGPS may be utilized in conjunction with route learning methodology, suchthat routes commonly traveled by a vehicle may be learned by the vehiclecontrol system 190. In some examples, other sensors, such as lasers,radar, sonar, acoustic sensors, etc., (e.g. 133) may be additionally oralternatively utilized in conjunction with the onboard navigation systemto conduct route learning of commonly traveled routes by the vehicle.

FIG. 2 shows a schematic depiction of a vehicle system 206. It may beunderstood that vehicle system 206 may comprise the same vehicle systemas vehicle system 100 depicted at FIG. 1. The vehicle system 206includes an engine system 208 coupled to an emissions control system(evaporative emissions system) 251 and a fuel system 218. It may beunderstood that fuel system 218 may comprise the same fuel system asfuel system 140 depicted at FIG. 1. Emission control system 251 includesa fuel vapor storage container or canister 222 which may be used tocapture and store fuel vapors. In some examples, vehicle system 206 maybe a hybrid electric vehicle system. However, it may be understood thatthe description herein may refer to a non-hybrid vehicle, for example avehicle only-equipped with an engine and not an onboard energy storagedevice, without departing from the scope of the present disclosure.

The engine system 208 may include an engine 110 having a plurality ofcylinders 230. The engine 110 includes an engine air intake 223 and anengine exhaust 225. The engine air intake 223 includes a throttle 262 influidic communication with engine intake manifold 244 via an intakepassage 242. Further, engine air intake 223 may include an air box andfilter (not shown) positioned upstream of throttle 262. The engineexhaust system 225 includes an exhaust manifold 248 leading to anexhaust passage 235 that routes exhaust gas to the atmosphere. Theengine exhaust system 225 may include one or more exhaust catalyst 270,which may be mounted in a close-coupled position in the exhaust. One ormore emission control devices may include a three-way catalyst, lean NOxtrap, diesel particulate filter, oxidation catalyst, etc. It will beappreciated that other components may be included in the engine such asa variety of valves and sensors. For example, a barometric pressuresensor 213 may be included in the engine intake. In one example,barometric pressure sensor 213 may be a manifold air pressure (MAP)sensor and may be coupled to the engine intake downstream of throttle262. Barometric pressure sensor 213 may rely on part throttle or full orwide open throttle conditions, e.g., when an opening amount of throttle262 is greater than a threshold, in order accurately determine BP.

Fuel system 218 may include a fuel tank 220 coupled to a fuel pumpsystem 221. It may be understood that fuel tank 220 may comprise thesame fuel tank as fuel tank 144 depicted above at FIG. 1. The fuel pumpsystem 221 may include one or more pumps for pressurizing fuel deliveredto the injectors of engine 110, such as the example injector 266 shown.While only a single injector 266 is shown, additional injectors areprovided for each cylinder. It will be appreciated that fuel system 218may be a return-less fuel system, a return fuel system, or various othertypes of fuel system. Fuel tank 220 may hold a plurality of fuel blends,including fuel with a range of alcohol concentrations, such as variousgasoline-ethanol blends, including E10, E85, gasoline, etc., andcombinations thereof. A fuel level sensor 234 located in fuel tank 220may provide an indication of the fuel level (“Fuel Level Input”) tocontroller 212. As depicted, fuel level sensor 234 may comprise a floatconnected to a variable resistor. Alternatively, other types of fuellevel sensors may be used.

Vapors generated in fuel system 218 may be routed to an evaporativeemissions control system 251 which includes a fuel vapor canister 222via vapor recovery line 231, before being purged to the engine airintake 223. Vapor recovery line 231 may be coupled to fuel tank 220 viaone or more conduits and may include one or more valves for isolatingthe fuel tank during certain conditions. For example, vapor recoveryline 231 may be coupled to fuel tank 220 via one or more or acombination of conduits 271, 273, and 275.

Further, in some examples, one or more fuel tank vent valves may bepositioned in conduits 271, 273, or 275. Among other functions, fueltank vent valves may allow a fuel vapor canister of the emissionscontrol system to be maintained at a low pressure or vacuum withoutincreasing the fuel evaporation rate from the tank (which wouldotherwise occur if the fuel tank pressure were lowered). For example,conduit 271 may include a grade vent valve (GVV) 287, conduit 273 mayinclude a fill limit venting valve (FLVV) 285, and conduit 275 mayinclude a grade vent valve (GVV) 283. Further, in some examples,recovery line 231 may be coupled to a fuel filler system 219. In someexamples, fuel filler system may include a fuel cap 205 for sealing offthe fuel filler system from the atmosphere. Refueling system 219 iscoupled to fuel tank 220 via a fuel filler pipe or neck 211.

Further, refueling system 219 may include refueling lock 245. In someexamples, refueling lock 245 may be a fuel cap locking mechanism. Thefuel cap locking mechanism may be configured to automatically lock thefuel cap in a closed position so that the fuel cap cannot be opened. Forexample, the fuel cap 205 may remain locked via refueling lock 245 whilepressure or vacuum in the fuel tank is greater than a threshold. Inresponse to a refuel request, e.g., a vehicle operator initiatedrequest, the fuel tank may be depressurized and the fuel cap unlockedafter the pressure or vacuum in the fuel tank falls below a threshold. Afuel cap locking mechanism may be a latch or clutch, which, whenengaged, prevents the removal of the fuel cap. The latch or clutch maybe electrically locked, for example, by a solenoid, or may bemechanically locked, for example, by a pressure diaphragm.

In some examples, refueling lock 245 may be a filler pipe valve locatedat a mouth of fuel filler pipe 211. In such examples, refueling lock 245may not prevent the removal of fuel cap 205. Rather, refueling lock 245may prevent the insertion of a refueling pump into fuel filler pipe 211.The filler pipe valve may be electrically locked, for example by asolenoid, or mechanically locked, for example by a pressure diaphragm.

In some examples, refueling lock 245 may be a refueling door lock, suchas a latch or a clutch which locks a refueling door located in a bodypanel of the vehicle. The refueling door lock may be electricallylocked, for example by a solenoid, or mechanically locked, for exampleby a pressure diaphragm.

In examples where refueling lock 245 is locked using an electricalmechanism, refueling lock 245 may be unlocked by commands fromcontroller 212, for example, when a fuel tank pressure decreases below apressure threshold. In examples where refueling lock 245 is locked usinga mechanical mechanism, refueling lock 245 may be unlocked via apressure gradient, for example, when a fuel tank pressure decreases toatmospheric pressure.

Emissions control system 251 may include one or more emissions controldevices, such as one or more fuel vapor canisters 222 filled with anappropriate adsorbent 286 b, the canisters are configured to temporarilytrap fuel vapors (including vaporized hydrocarbons) during fuel tankrefilling operations and “running loss” (that is, fuel vaporized duringvehicle operation). In one example, the adsorbent 286 b used isactivated charcoal. Emissions control system 251 may further include acanister ventilation path or vent line 227 which may route gases out ofthe canister 222 to the atmosphere when storing, or trapping, fuelvapors from fuel system 218.

Canister 222 may include a buffer 222 a (or buffer region), each of thecanister and the buffer comprising the adsorbent. As shown, the volumeof buffer 222 a may be smaller than (e.g., a fraction of) the volume ofcanister 222. The adsorbent 286 a in the buffer 222 a may be same as, ordifferent from, the adsorbent in the canister (e.g., both may includecharcoal). Buffer 222 a may be positioned within canister 222 such thatduring canister loading, fuel tank vapors are first adsorbed within thebuffer, and then when the buffer is saturated, further fuel tank vaporsare adsorbed in the canister. In comparison, during canister purging,fuel vapors are first desorbed from the canister (e.g., to a thresholdamount) before being desorbed from the buffer. In other words, loadingand unloading of the buffer is not linear with the loading and unloadingof the canister. As such, the effect of the canister buffer is to dampenany fuel vapor spikes flowing from the fuel tank to the canister,thereby reducing the possibility of any fuel vapor spikes going to theengine. One or more temperature sensors 232 may be coupled to and/orwithin canister 222. As fuel vapor is adsorbed by the adsorbent in thecanister, heat is generated (heat of adsorption). Likewise, as fuelvapor is desorbed by the adsorbent in the canister, heat is consumed. Inthis way, the adsorption and desorption of fuel vapor by the canistermay be monitored and estimated based on temperature changes within thecanister.

Vent line 227 may also allow fresh air to be drawn into canister 222when purging stored fuel vapors from fuel system 218 to engine intake223 via purge line 228 and purge valve 261. For example, purge valve 261may be normally closed but may be opened during certain conditions sothat vacuum from engine intake manifold 244 is provided to the fuelvapor canister for purging. In some examples, vent line 227 may includean air filter 259 disposed therein upstream of a canister 222.

In some examples, the flow of air and vapors between canister 222 andthe atmosphere may be regulated by a canister vent valve 297 coupledwithin vent line 227. When included, the canister vent valve 297 may bea normally open valve, so that fuel tank isolation valve 252 (FTIV) maycontrol venting of fuel tank 220 with the atmosphere. FTIV 252 may bepositioned between the fuel tank and the fuel vapor canister 222 withinconduit 278. FTIV 252 may be a normally closed valve, that when opened,allows for the venting of fuel vapors from fuel tank 220 to fuel vaporcanister 222. Fuel vapors may then be vented to atmosphere, or purged toengine intake system 223 via canister purge valve 261.

Fuel system 218 may be operated by controller 212 in a plurality ofmodes by selective adjustment of the various valves and solenoids. Itmay be understood that control system 214 may comprise the same controlsystem as control system 190 depicted above at FIG. 1. For example, thefuel system may be operated in a fuel vapor storage mode (e.g., during afuel tank refueling operation and with the engine not combusting air andfuel), wherein the controller 212 may open isolation valve 252 (whenincluded) while closing canister purge valve (CPV) 261 to directrefueling vapors into canister 222 while preventing fuel vapors frombeing directed into the intake manifold.

As another example, the fuel system may be operated in a refueling mode(e.g., when fuel tank refueling is requested by a vehicle operator),wherein the controller 212 may open isolation valve 252 (when included),while maintaining canister purge valve 261 closed, to depressurize thefuel tank before allowing enabling fuel to be added therein. As such,isolation valve 252 (when included) may be kept open during therefueling operation to allow refueling vapors to be stored in thecanister. After refueling is completed, the isolation valve may beclosed.

As yet another example, the fuel system may be operated in a canisterpurging mode (e.g., after an emission control device light-offtemperature has been attained and with the engine combusting air andfuel), wherein the controller 212 may open canister purge valve 261while closing isolation valve 252 (when included). Herein, the vacuumgenerated by the intake manifold of the operating engine may be used todraw fresh air through vent 227 and through fuel vapor canister 222 topurge the stored fuel vapors into intake manifold 244. In this mode, thepurged fuel vapors from the canister are combusted in the engine. Thepurging may be continued until the stored fuel vapor amount in thecanister is below a threshold.

Controller 212 may comprise a portion of a control system 214. In someexamples, control system 214 may be the same as control system 190,illustrated in FIG. 1. Control system 214 is shown receiving informationfrom a plurality of sensors 216 (various examples of which are describedherein) and sending control signals to a plurality of actuators 281(various examples of which are described herein). As one example,sensors 216 may include exhaust gas sensor 237 located upstream of theemission control device 270, temperature sensor 233, pressure sensor291, pressure sensor 282, and canister temperature sensor 232. Othersensors such as pressure, temperature, air/fuel ratio, and compositionsensors may be coupled to various locations in the vehicle system 206.As another example, the actuators may include throttle 262, fuel tankisolation valve 252, canister purge valve 261, and canister vent valve297. The control system 214 may include a controller 212. The controllermay receive input data from the various sensors, process the input data,and trigger the actuators in response to the processed input data basedon instruction or code programmed therein corresponding to one or moreroutines. Example control routines are described herein with regard toFIG. 3 and FIG. 9.

In some examples, the controller may be placed in a reduced power modeor sleep mode, wherein the controller maintains essential functionsonly, and operates with a lower battery consumption than in acorresponding awake mode. For example, the controller may be placed in asleep mode following a vehicle-off event in order to perform adiagnostic routine at a duration after the vehicle-off event. Thecontroller may have a wake input that allows the controller to bereturned to an awake mode based on an input received from one or moresensors.

Undesired evaporative emissions detection routines may be intermittentlyperformed by controller 212 on fuel system 218 and/or evaporativeemissions system 251 to confirm that undesired evaporative emissions arenot present in the fuel system and/or evaporative emissions system. Assuch, evaporative emissions detection routines may be performed whilethe engine is off (engine-off test) using engine-off natural vacuum(EONV) generated due to a change in temperature and pressure at the fueltank following engine shutdown and/or with vacuum supplemented from avacuum pump. Alternatively, evaporative emissions detection routines maybe performed while the engine is running by operating a vacuum pump(where included) and/or using engine intake manifold vacuum. In someconfigurations, a canister vent valve (CVV) 297 may be coupled withinvent line 227. CVV 297 may function to adjust a flow of air and vaporsbetween canister 222 and the atmosphere. The CVV may also be used fordiagnostic routines. When included, the CVV may be opened during fuelvapor storing operations (for example, during fuel tank refueling andwhile the engine is not running) so that air, stripped of fuel vaporafter having passed through the canister, can be pushed out to theatmosphere. Likewise, during purging operations (for example, duringcanister regeneration and while the engine is running), the CVV may beopened to allow a flow of fresh air to strip the fuel vapors stored inthe canister. In some examples, CVV 297 may be a solenoid valve whereinopening or closing of the valve is performed via actuation of a canistervent solenoid. In particular, the canister vent valve may be an openthat is closed upon actuation of the canister vent solenoid. In someexamples, CVV 297 may be configured as a latchable solenoid valve. Inother words, when the valve is placed in a closed configuration, itlatches closed without requiring additional current or voltage. Forexample, the valve may be closed with a 100 ms pulse, and then opened ata later time point with another 100 ms pulse. In this way, the amount ofbattery power required to maintain the CVV closed is reduced. Inparticular, the CVV may be closed while the vehicle is off, thusmaintaining battery power while maintaining the fuel emissions controlsystem sealed from atmosphere.

Conducting an EONV test may include four “phases”. The first phase maycomprise an initial vent phase. This initial vent phase is conducted tovent any vapors from a fuel slosh event from a hard stop just prior tokey off. The initial vent phase may comprise 30-60 seconds, for example.The next phase of the EONV test may constitute a pressure phase. In thisphase, the fuel system and evaporative emissions systems are sealed fromatmosphere, and a pressure build is monitored over time. If the pressurein the fuel system and evaporative emissions system reaches a positivepressure threshold, an absence of undesired evaporative emissions may beindicated. However, if the pressure build stalls (e.g. plateaus), thenthe pressure in the fuel system and evaporative emissions system may berelieved, during what is referred to as the vent phase. After pressurein the fuel tank and evaporative emissions system is relieved, a vacuumphase comes next. The vacuum phase may include re-sealing the fuelsystem and evaporative emissions system, and monitoring a vacuum buildover time. If vacuum builds to a negative pressure threshold within apredetermined duration (e.g. 45 minutes since the start of the EONVtest), then an absence of undesired evaporative emissions may beindicated.

In some examples where the vehicle includes a sealed fuel tank, standingpressure in the sealed fuel tank may be indicative of an absence ofundesired evaporative emissions. For example, if pressure greater than(e.g. more positive or more negative than) a predetermined absolutepressure threshold is indicated in the fuel tank, then the absence ofundesired evaporative emissions may be indicated. However, if there isan inherent offset associated with the FTPT, then there may becircumstances where the presence of undesired evaporative emissions inthe fuel system may be incorrectly diagnosed as an absence of undesiredevaporative emissions.

Furthermore, as discussed above, an inherent offset associated with theFTPT may result in a fuel door or other refueling lock associated withaccessing a fuel filler neck (e.g. 211) unable to be opened, due to anindication of pressure in the fuel system, where in fact the fuel systemmay be at atmospheric pressure. However, there may be other reasons forthe fuel system not depressurizing, such as a stuck closed FTIV, forexample. It is herein recognized that under such a circumstance wherethe fuel lock does not open due to an indication that the fuel system isnot sufficiently depressurized, if the fuel lock is unlocked manually,the ensuing refueling event may provide an opportunity to diagnose thereason as to why the fuel lock did not open until it was manuallyopened. For example, the FTPT may have an inherent offset or may bestuck in range, or the FTIV may be stuck closed. The method discussedbelow at FIG. 3 may enable a determination as to which may be the casefor the particular situation.

Turning now to FIG. 3, an example method 300 for diagnosing a vehiclefuel system during a refueling event, is shown. Specifically, method 300may be used to diagnose whether a standing pressure in the vehicle fuelsystem is due to an FTPT offset or otherwise degraded FTPT, or to astuck closed FTIV and/or restriction or blockage in one or more linescoupling the fuel system to atmosphere. Method 300 may be used during arefueling event where it is indicated that the fuel filler neck has beenaccessed manually, for example via a button (e.g. 191) in a trunk of thevehicle.

Method 300 will be described with reference to the systems describedherein and shown in FIGS. 1-2, though it should be understood thatsimilar methods may be applied to other systems without departing fromthe scope of this disclosure. Method 300 may be carried out by acontroller, such as controller 212 in FIG. 2, and may be stored at thecontroller as executable instructions in non-transitory memory.Instructions for carrying out method 300 and the rest of the methodsincluded herein may be executed by the controller based on instructionsstored on a memory of the controller and in conjunction with signalsreceived from sensors of the engine system, such as the sensorsdescribed above with reference to FIGS. 1-2. The controller may employactuators such as FTIV (e.g. 252), etc., to alter states of devices inthe physical world according to the method depicted below.

Method 300 begins at 305, and includes estimating and/or measuringvehicle operating conditions. Operating conditions may be estimated,measured, and/or inferred, and may include one or more vehicleconditions, such as vehicle speed, vehicle location, etc., variousengine conditions, such as engine status, engine load, engine speed, A/Fratio, manifold air pressure, etc., various fuel system conditions, suchas fuel level, fuel type, fuel temperature, etc., various evaporativeemissions system conditions, such as fuel vapor canister load, fuel tankpressure, etc., as well as various ambient conditions, such as ambienttemperature, humidity, barometric pressure, etc.

Proceeding to 310, method 300 may include indicating whether refuelingis requested by a vehicle operator. For example, refueling may beindicated to be requested if a refueling button (e.g. 197) associatedwith the vehicle instrument panel (e.g. 196) has been depressed. It maybe understood that such a request may not unlock a refueling lock (e.g.145), but may only signal the request to refuel, which may then beenabled in response to pressure in the fuel system becoming within athreshold (e.g. +/−5 InH2O) of atmospheric pressure.

If refueling is not requested, method 300 may proceed to 315. At 315,method 300 may include maintaining current vehicle operating parameters.For example, if the vehicle is operating via an electric-only mode, thensuch a mode of operation may be maintained. If the vehicle is operatingvia the engine, or some combination of the engine and the electricalmode of operation, then such operation may be maintained. Method 300 maythen end.

Returning to 310, in response to refueling being indicated to berequested, method 300 may proceed to 320. At 320, method 300 may includecommanding open the FTIV. While not explicitly illustrated, commandingopen the FTIV at 320 may further include commanding open or maintainingopen the CVV (e.g. 297), such that the fuel system is fluidicallycoupled to atmosphere (provided the FTIV is functioning as desired).

It may be understood that with the fuel system coupled to atmosphere, itmay be expected that pressure in the fuel system may decrease to withinthe threshold of atmospheric pressure. However, in a case where the FTPT(e.g. 291) has an inherent offset, or in a case where the FTIV did notopen as expected (or where there are other restrictions in the linescoupling the fuel system to atmosphere), then pressure may not decreaseto within the threshold of atmospheric pressure. In such an example, thefuel filler neck may be prevented from being accessed, or in otherwords, the refueling lock (e.g. 245) may be maintained locked.

Accordingly, proceeding to 325, method 300 may include indicatingwhether the fuel filler neck was accessed manually or not. Specifically,in response to the refueling lock not opening due to pressure notdecreasing to within the threshold of atmospheric pressure, a vehicleoperator may manually unlock the refueling lock (which may for examplecomprise a fuel door lock), by depressing a manual refueling lock button(e.g. 191) positioned in a trunk of the vehicle, for example. The manualrefueling lock is mentioned as being in the trunk, but may be anywherein such a vehicle without departing from the scope of this disclosure.

Thus, in a case where the fuel filler neck is not indicated to beaccessed manually, it may be understood that upon commanding open theFTIV, the fuel tank depressurized to within the threshold of atmosphericpressure thus resulting in the unlocking of the refueling lock to enablefuel to be added to the fuel system. Accordingly, in such an example,method 300 may proceed from 325 to 330, where refueling may proceed. At330, the vehicle operator or gas station attendant may dispense adesired amount of fuel to the fuel tank, and afterward, with a desiredamount of fuel having been added to the tank, method 300 may end. Whilenot explicitly illustrated, it may be understood that in a case wherethe fuel system did not depressurize, but where the vehicle operatordecides to drive off rather than manually open the refueling lock, thenmethod 300 may be aborted.

Returning to 325, if the fuel filler neck is indicated to have beenaccessed manually, method 300 may proceed to 335. At 335, method 300 mayinclude monitoring fuel system pressure and fuel level during refuelingof the fuel tank. Fuel system pressure and fuel level may be monitoredsuch that a diagnosis of whether the FTPT has an inherent offset,whether the FTPT is stuck in range, or whether the FTIV is stuck closedor if other restrictions are present, may be indicated. Accordingly,such a diagnosis may be made via the lookup table at FIG. 4. It may beunderstood that the lookup table depicted at FIG. 4 for diagnosing fuelsystem integrity depends on both the fuel system pressure and the fuellevel during refueling of the fuel tank.

Accordingly, turning now to FIG. 4, an example lookup table 400 isdepicted. Lookup table 400 includes an outcome 405 (outcomes A-C),symptoms 410 for each possible outcome, a diagnosis 415 based on theparticular symptoms, and mitigating actions 420 that may be taken foreach particular outcome.

Briefly, outcome A may include an indication that the FTPT sensorreports pressure decaying to atmospheric pressure just prior (e.g. lessthan 1 minute, or less than 30 seconds) to fuel level increasing, butwhere the ensuing refueling event is plagued with one or more prematureshutoff events of a refueling dispenser that is dispensing fuel to thefuel tank. In such a case, the diagnosis may include a determinationthat the FTPT is functioning as desired, but that the FTIV is stuckclosed (or that there is some other restriction preventingdepressurization). More specifically, because the refueling lock wasmanually opened, with the refueling dispenser placed in the fuel fillerneck, the fuel tank may at least partially become coupled to atmosphere.Thus, if the FTPT were functioning as desired, then once the refuelingdispenser is placed in the fuel filler neck, pressure may be expected torapidly approach atmospheric pressure. If the FTIV is stuck closedand/or if there is a restriction in the line coupling the fuel tank tothe fuel vapor storage canister and/or a restriction in the vent linecoupling the canister to atmosphere, then any attempt to refuel may beexpected to result in premature shutoffs of the refueling dispenser.Accordingly, a rapid decay to atmospheric pressure upon insertion of thefuel dispenser into the fuel filler neck, followed by one or morepremature shutoffs, may comprise outcome A, or in other words, anindication that the FTPT is functioning as desired or expected, and thatthe FTIV is stuck closed (or there is some other restriction in thelines coupling the fuel tank to atmosphere).

In such an example, mitigating action may include illuminating amalfunction indicator light (MIL) at the vehicle dash, to alert thevehicle operator of a request to service the vehicle. A diagnostictrouble code (DTC) may be set, and stored at the controller, indicatingthe issue of the stuck closed FTIV and/or restriction. Because of theinability to refuel without premature shutoffs, the vehicle may beoperated in such a way as to reduce opportunity where the vehicle mayhave to be refueled. Specifically, the vehicle may be operated inelectric-only mode as frequently as possible, until the issue has beenresolved. Furthermore, any tests for undesired evaporative emissions onthe fuel system and/or evaporative emissions system that rely onevacuating the fuel system and/or evaporative emissions system, may bediscontinued until the issue is mitigated.

Outcome B depicts a situation where the refueling lock was manuallyopened, and where pressure in the fuel system does not change eitherjust prior to or during the addition of fuel to the tank. The refuelingevent may proceed without premature shutoffs of the refueling dispenser,and fuel level may linearly increase over the course of the refuelingevent. In such an example, the FTPT may be stuck in range or in otherwords, not moving or registering any change in pressure, and thus may beunderstood to be degraded. Furthermore, for such an outcome, the FTIVmay be indicated to be functioning as desired, and an absence ofrestrictions may be indicated in the lines that couple the fuel systemto atmosphere.

Mitigating action for such an outcome B may include illuminating a MILat the dash to alert the vehicle operator of a request to service thevehicle, and a DTC may be set related to the degraded FTPT, and may bestored at the controller. A flag may be set at the controller,indicating that refueling was requested, but that in order to do so, therefueling lock had to be manually unlocked. If such an event occurs morethan a predetermined number of times (e.g. three or more) where therefueling lock has to be manually opened, then control strategy may bemodified to enable the refueling lock to be unlocked in response to arequest for refueling, regardless of pressure in the tank. In otherwords, in response to a request to refuel after the predetermined numberof times the refueling lock was manually opened, the refueling lock maybe opened without the vehicle operator having to manually open the lock.In other words, the controller may alter the strategy such that therequest to refuel (e.g. pressing of button 197) may command unlocked therefueling lock, without reliance on fuel system depressurization.

Furthermore, because the FTPT is stuck in range, any tests for presenceor absence of undesired evaporative emissions that rely on the FTPT, maybe postponed until mitigating action is undertaken to resolve the issuewith the FTPT.

Outcome C depicts a situation where the refueling event initiated with aparticular offset that did not decay to atmospheric pressure just afterinserting the refueling dispenser and prior to fuel level in the fueltank rising. Instead, Outcome C depicts a situation where pressure risesto a steady state that is greater than the initial offset, and wherefuel level in the fuel tank rises linearly without premature shutoffs.Accordingly, Outcome C is diagnosed as a situation where the FTPT has aninherent offset, but where there are no restrictions in the linescoupling the fuel tank to atmosphere and where the FTIV is not stuckclosed.

With an inherent offset diagnosed as per outcome C, mitigating actionmay include illuminating a MIL at the dash, alerting the vehicleoperator of a request to service the vehicle. A DTC may be set at thecontroller, reflecting the FTPT with the inherent offset. Mitigatingaction for outcome C may include setting a flag at the controller toreflect the inherent offset, such that if the refueling lock is manuallyunlocked a predetermined number of times (e.g. 3 or more), then thecontroller may alter its strategy to enable the refueling lock unlockedin response to a request to refuel, rather than having to manuallyunlock the refueling lock. In some examples, the refueling lock may beunlocked in response to a request to refuel provided that pressure inthe fuel system is within a threshold (e.g. +/−5 InH2O) of thedetermined offset. For example, if the offset is determined to be 7InH2O (where 7 InH2O as registered via the FTPT corresponds toatmospheric pressure due to the inherent offset), then the refuelinglock may be unlocked responsive to pressure in the fuel system beinganywhere from 2 InH2O to 12 InH2O.

Because for outcome C the FTPT offset is determined/known, the offsetmay be relied upon for any determination of a presence of absence ofundesired evaporative emissions stemming from the fuel system. Forexample, if a fuel system pressure corresponding to 6 InH2O or greater(as an example) is used as an indication that a sealed fuel system isfree from a source of undesired evaporative emissions, and there is aninherent offset of 8 InH2O, then when pressure is at 8 InH2O the fuelsystem may be indicated to be free from undesired evaporative emissions,when in fact there may be a source of undesired evaporative emissionsstemming from the fuel system, if the offset is not accounted for.Accordingly, for outcome C, the inherent offset may be corrected for inthe control strategy, such that (as per the above example) atmosphericpressure may correspond to the offset (8 InH2O), and thresholds forindicating a presence of undesired evaporative emissions may becorrespondingly adjusted. For example, undesired evaporative emissionsmay be indicated if pressure in the sealed fuel system during adiagnostic for presence or absence of undesired evaporative emissions is8 InH2O+/−6 InH2O. In other words, the inherent offset may becomeatmospheric pressure, and the thresholds may be set as +/−6 InH2O ofatmospheric pressure (where atmospheric pressure corresponds to theinherent offset).

The above example relates to a situation where the fuel system is sealed(e.g. FTIV closed), and standing pressure greater than a thresholdpressure (e.g. above 6 InH2O or below −6 InH2O) is used to indicatepresence or absence of undesired evaporative emissions. However, theremay be other tests for undesired evaporative emissions for whichthreshold(s) may be adjusted in response to a determination of an FTPToffset. In one example, a test for presence or absence of undesiredevaporative emissions may include the fuel system and/or evaporativeemissions system being evacuated via engine manifold vacuum, and inresponse to a predetermined threshold negative pressure being reached,the fuel system and/or evaporative emissions system may be sealed fromatmosphere and a pressure bleed-up monitored. If pressure in the sealedfuel system and/or evaporative emissions system remains below a pressurebleed-up threshold (and/or if a pressure bleed-up rate is below apressure bleed-up rate threshold), then an absence of undesiredevaporative emissions may be indicated. An inherent offset of the FTPTmay result in situations where a source of undesired evaporativeemissions are indicated when in reality, the fuel system and/orevaporative emissions system is free from a source of undesiredevaporative emissions. Alternatively, an inherent offset of the FTPT mayresult in situations where undesired evaporative emissions are notindicated, but should be, where the inherent offset is not accountedfor. Thus, a determination of an inherent offset of the FTPT may be usedto adjust the negative pressure threshold for evacuating the fuel systemand/or evaporative emissions system, and may additionally be used toadjust the pressure bleed-up threshold (and pressure bleed-up ratethreshold) for such types of test for undesired evaporative emissions.

Another example of a test for presence of absence of undesiredevaporative emissions is based on heat rejection from an engine at avehicle-off event, and is referred to (as discussed above) as an EONVtest. As discussed, such a test includes a phase where a pressure buildin the fuel system is monitored and if a positive pressure threshold isreached, then undesired evaporative emissions are not indicated. If thepositive pressure threshold is not reached, then a vacuum-phase may beconducted where pressure in the fuel system is monitored as the fuelsystem cools and if a negative pressure threshold is reached, thenundesired evaporative emissions are not indicated. Of course, an FTPTwith an inherent offset may result in a vehicle fuel system beingindicated to be free from undesired evaporative emissions when in fact,the positive pressure threshold and/or negative pressure threshold wasonly reached because of the offset. Thus, in such a case, if FTPT offsetis used to appropriately adjust the positive pressure and negativepressure thresholds, then incorrect indications as related to presenceor absence of undesired evaporative emissions may be avoided.

In regards to the EONV-type test described above, in a situation whereFTPT offset is indicated to be 10 InH2O, then the positive pressurethreshold may be increased by 10 InH2O, and the negative pressurethreshold may be made less negative by 10InH2O. In this way, an accurateindication as to presence of absence of undesired evaporative emissionsmay be indicated for such a test diagnostic.

Returning to FIG. 3, upon diagnosing fuel system degradation based onfuel system pressure and fuel fill level at 340, method 300 may proceedto 345. At 345, method 300 may include proceeding with refueling wherepossible. For example, outcome A may allow for a limited amount ofrefueling, as the refueling may be plagued with premature shutoffs.Alternatively, both outcomes B and C may allow for the fuel tank to berefueled without premature shutoffs.

Proceeding to step 350, method 300 may include updating vehicleoperating conditions and may further include taking mitigating action.For example, updating vehicle operating conditions may include settingMILs and/or DTCs, and may further include taking the mitigating actionas detailed above at FIG. 4. Method 300 may then end.

Turning now to FIG. 5A, an example timeline 500 is depicted,illustrating outcome A as depicted at FIG. 4, as determined via themethod of FIG. 3. Timeline 500 includes plot 505, indicating whetherrefueling is requested (yes or no), over time. It may be understood thata refuel request as per plot 505 includes a vehicle operator depressinga refueling button (e.g. 197) at the dash (e.g. 196). It may be furtherunderstood that such a request does not automatically result in therefueling lock (e.g. 245) being unlocked. Timeline 500 further includesplot 510, indicating fuel system pressure as monitored via an FTPT (e.g.291). Line 511 represents atmospheric pressure, and line 512 representsa predetermined threshold away from atmospheric pressure, where, ifbelow, the fuel system may be indicated to be depressurized. While notexplicitly illustrated, another predetermined threshold may be belowatmospheric pressure, the same amount away from atmospheric pressure asline 512. Timeline 500 further includes plot 515, indicating fuel levelin a fuel tank of the fuel system. Fuel level may be monitored via afuel level indicator (FLI) (e.g. 234), and may increase (+) or decrease(−) over time. Timeline 500 further includes plot 520, indicating astatus of an FTIV (e.g. 252), over time. The FTIV may be eithercommanded fully open or fully closed, over time. Timeline 500 furtherincludes plot 525, indicating whether the refueling lock (e.g. 245) hasbeen manually unlocked (yes or no), over time. As discussed above,manually unlocking the refueling lock may include depression of a manualrefueling lock button (e.g. 191) positioned for example in a trunk ofthe vehicle.

At time t0, while not explicitly illustrated it may be understood thatthe vehicle is in motion, and is traveling to a refueling station.Accordingly, refueling has not yet been requested (plot 505), pressurein the fuel tank is above atmospheric pressure (plot 510), and fuellevel in the tank is relatively low (plot 515). The FTIV is closed (plot520), and the refueling lock has not been manually unlocked (plot 525).

At time t1, refueling is requested (plot 505). Accordingly, at time t2,the FTIV is commanded open to depressurize the fuel system, prior toenabling refueling to commence (prior to unlocking the refueling lock).However, between time t2 and t3, pressure in the fuel system does notdecline. With pressure in the fuel system not declining, it may beunderstood that the refueling lock remains locked. Accordingly, at timet3, the refueling lock is manually unlocked via the vehicle operator(plot 525).

In response to the refueling lock being manually unlocked, between timet3 and t4, pressure in the fuel system decays to atmospheric pressure,represented by line 511. Thus, between time t3 and t4 it may beunderstood that a refueling nozzle was inserted into the fuel fillerneck, thus coupling the fuel system to atmosphere, and as a resultpressure in the fuel system rapidly decayed to atmospheric pressure.Between time t4 and t5, pressure in the fuel system steadily rises (plot510) and fuel level increases (plot 515), yet at time t5, pressure inthe fuel system peaks and then rapidly declines between time t5 and t6.Furthermore, fuel level stabilizes and does not rise further betweentime t5 and t6. Thus, it may be understood that at time t5 a prematureshutoff of the refueling dispenser occurred due to pressure in the fuelsystem rising to a point where it induced automatic shutoff of therefueling dispenser.

Between time t6 and t7, pressure in the fuel system again rises andpeaks (plot 510), and fuel is again dispensed into the fuel tank (plot515). At time t7, another premature shutoff of the refueling dispenseris induced, thus between time t7 and t8 pressure in the fuel systemagain rapidly declines and fuel ceases to be added to the fuel tank.Between time t8 and t9, pressure again rises in the fuel system (plot510) and fuel is once again dispensed into the fuel tank (plot 515). Attime t9, another premature shutoff of the refueling dispenser isinduced, thus between time t9 and t10 pressure in the fuel systemrapidly declines and fuel is no longer dispensed into the fuel tank. Nofurther attempts at dispensing fuel into the fuel tank are attemptedafter time t10. With the fuel system at atmospheric pressure, the FTIVis commanded closed. While not explicitly illustrated, it may beunderstood that by time t11, the refueling lock is again locked, andthus refueling is no longer requested (plot 505) and the refueling lockis thus no longer indicated to be manually unlocked (plot 525).

Thus, timeline 500 indicates outcome A as depicted at FIG. 4, because itwas observed that pressure in the fuel system rapidly decayed toatmospheric pressure between time t3 and t4 in response to the refuelingdispenser being inserted into the fuel filler neck, and that subsequentattempts to refuel the fuel tank included a number of premature shutoffsof the refueling dispenser. Thus, such a timeline indicates a situationwhere the FTPT is functioning as desired but where the FTIV is eitherstuck closed or there is a restriction in one of the lines coupling thefuel system to atmosphere during the refueling event.

Turning now to FIG. 5B, another example timeline 540 is depicted.Timeline 540 depicts example outcome B, as discussed above at FIG. 4.Timeline 540 includes plot 545, indicating whether refueling isrequested (yes or no), over time. It may be understood that a refuelrequest as per plot 545 includes a vehicle operator depressing arefueling button (e.g. 197) at the dash (e.g. 196). It may be furtherunderstood that such a request does not automatically result in therefueling lock (e.g. 245) being unlocked. Timeline 540 further includesplot 550, indicating fuel system pressure as monitored via an FTPT (e.g.291). Line 551 represents atmospheric pressure, and lines 552 and 553represent predetermined thresholds away from atmospheric pressure,where, if pressure is below plot 553 and above plot 552, the fuel systemmay be indicated to be depressurized. In other words, if pressure isbetween lines 552 and 553, then the fuel system may be determined to bedepressurized. Timeline 540 further includes plot 555, indicating fuellevel in a fuel tank of the fuel system. Fuel level may be monitored viaa fuel level indicator (FLI) (e.g. 234), and may increase (+) ordecrease (−) over time. Timeline 540 further includes plot 560,indicating a status of an FTIV (e.g. 252), over time. The FTIV may beeither commanded fully open or fully closed, over time. Timeline 540further includes plot 565, indicating whether the refueling lock (e.g.245) has been manually unlocked (yes or no), over time. As discussedabove, manually unlocking the refueling lock may include depression of amanual refueling lock button (e.g. 191) positioned for example in atrunk of the vehicle.

At time t0, while not explicitly illustrated it may be understood thatthe vehicle is in motion, and is traveling to a refueling station.Accordingly, refueling has not yet been requested (plot 545), pressurein the fuel tank is above atmospheric pressure (plot 550), and fuellevel in the tank is relatively low (plot 555). The FTIV is closed (plot560), and the refueling lock has not been manually unlocked (plot 565).

At time t1, refueling is requested (plot 545). Accordingly, at time t2,the FTIV is commanded open to depressurize the fuel system, prior toenabling refueling to commence (prior to unlocking the refueling lock).However, between time t2 and t3, pressure in the fuel system does notdecline. With pressure in the fuel system not declining, it may beunderstood that the refueling lock remains locked. Accordingly, at timet3, the refueling lock is manually unlocked via the vehicle operator(plot 525).

In response to the refueling lock being manually unlocked, between timet3 and t4 pressure in the fuel system does not decay to atmosphericpressure, represented by line 551. However, at time t4 fuel level in thefuel tank begins to rise, and between time t4 and t5, fuel level in thefuel tank linearly increases. Thus, it may be understood that althoughthe refueling dispenser was placed in the fuel filler neck thus couplingthe fuel system to atmospheric pressure, pressure in the fuel system didnot decay, and furthermore, pressure did not change upon fuel beingadded to the tank between time t4 and t5. Because no premature shutoffsof the refueling dispenser are indicated between time t4 and t5, theissue of why the fuel tank did not initially depressurize cannot beattributed to the FTIV being stuck closed, or to restrictions in thelines coupling the fuel system to atmosphere. Instead, the reason forthe lack of depressurization of the fuel tank is because the FTPT isstuck in range as discussed above with regard to FIG. 4, outcome B.

Between time t5 and t6, no further fuel is dispensed, and while notexplicitly illustrated, it may be understood that the refueling lock isonce again locked, and accordingly, refueling is no longer requested(plot 545), the FTIV is commanded closed (plot 560) and the refuel lockis no longer indicated to be manually unlocked (plot 565).

Turning now to FIG. 5C, another example timeline 570 is depicted.Timeline 570 depicts example outcome C, as discussed above at FIG. 4.Timeline 570 includes plot 575, indicating whether refueling isrequested (yes or no), over time. It may be understood that a refuelrequest as per plot 575 includes a vehicle operator depressing arefueling button (e.g. 197) at the dash (e.g. 196). It may be furtherunderstood that such a request does not automatically result in therefueling lock (e.g. 245) being unlocked. Timeline 570 further includesplot 580, indicating fuel system pressure as monitored via an FTPT (e.g.291). Line 581 represents atmospheric pressure, and lines 582 and 583represent predetermined thresholds away from atmospheric pressure,where, if below plot 583 or above plot 582, the fuel system may beindicated to be depressurized. In other words, if pressure is betweenlines 582 and 583, then the fuel system may be determined to bedepressurized. Timeline 570 further includes plot 585, indicating fuellevel in a fuel tank of the fuel system. Fuel level may be monitored viaa fuel level indicator (FLI) (e.g. 234), and may increase (+) ordecrease (−) over time. Timeline 570 further includes plot 590,indicating a status of an FTIV (e.g. 252), over time. The FTIV may beeither commanded fully open or fully closed, over time. Timeline 570further includes plot 595, indicating whether the refueling lock (e.g.245) has been manually unlocked (yes or no), over time. As discussedabove, manually unlocking the refueling lock may include depression of amanual refueling lock button (e.g. 191) positioned for example in atrunk of the vehicle.

At time t0, while not explicitly illustrated it may be understood thatthe vehicle is in motion, and is traveling to a refueling station.Accordingly, refueling has not yet been requested (plot 575), pressurein the fuel tank is above atmospheric pressure (plot 580), and fuellevel in the tank is relatively low (plot 585). The FTIV is closed (plot590), and the refueling lock has not been manually unlocked (plot 595).

At time t1, refueling is requested (plot 575). Accordingly, at time t2,the FTIV is commanded open to depressurize the fuel system, prior toenabling refueling to commence (prior to unlocking the refueling lock).However, between time t2 and t3, pressure in the fuel system does notdecline. With pressure in the fuel system not declining, it may beunderstood that the refueling lock remains locked. Accordingly, at timet3, the refueling lock is manually unlocked via the vehicle operator(plot 595).

In response to the refueling lock being manually unlocked, between timet3 and t4, pressure in the fuel system does not decay to atmosphericpressure, represented by line 551. However, at time t4 fuel level in thefuel tank begins to rise, and between time t4 and t5, fuel level in thefuel tank linearly increases. Thus, it may be understood that althoughthe refueling dispenser was placed in the fuel filler neck thus couplingthe fuel system to atmospheric pressure, pressure in the fuel system didnot decay. However, as fuel is dispensed into the fuel tank between timet4 and t5, pressure in the fuel system increases from the value it wasprior to fuel being added to the fuel tank, and stabilizes at a newhigher pressure level (plot 580). At time t5 it may be understood thatthe refueling dispenser is withdrawn from the fuel filler neck (withoutan automatic shutoff being induced). Thus, no further fuel is dispensedbetween time t5 and t6, and pressure rapidly decays to the offset valuethe pressure was at prior to the fuel tank receiving fuel from thedispenser (plot 580). While not explicitly illustrated, the refuelinglock is re-locked just prior to time t6. At time t6, refueling is nolonger requested, the FTIV is commanded closed, and the refueling lockis no longer indicated to be manually unlocked.

Accordingly, timeline 540 illustrates a situation corresponding tooutcome C, where there is an inherent offset in the FTPT, but otherwisethe FTPT is functioning as desired, and there are no indications thatthe FTIV is stuck closed and/or that there are any restrictions in thelines coupling the fuel system to atmosphere. It may be understood thatthe offset corresponding to the amount above atmospheric pressure asread by the FTPT while the fuel system is coupled to atmosphericpressure (between time t2-t4) may be used to compensate any tests forpresence or absence of undesired evaporative emissions that rely on theFTPT. Furthermore, as discussed above the offset may be used toreconfigure control strategy for depressurizing the fuel system, suchthat the offset value may correspond to atmospheric pressure, and thefuel system may be indicated as being depressurized when pressure in thefuel system is within +/−5 InH2O of the offset value. This may enablethe refueling lock to be unlocked in response to the request forrefueling, without the vehicle operator having to manually unlock therefueling lock. In some examples, compensation whereby a request forrefueling (without having to manually unlock the refueling lock) may besufficient to command the refueling lock unlocked may be establishedafter a predetermined number of times (e.g. 3) that the vehicle operatormanually has to unlock the refueling lock to commence refueling. Morespecifically, after the predetermined number of times that the refuelinglock has to be manually unlocked in response to a request to refuel,then control strategy may be modified such that the act of requestingrefueling (e.g. pressing of button 197) may trigger the refueling lockunlocked, without reliance on the FTPT, in some examples.

While a refueling event may comprise an event whereby the FTPT may berationalized and any inherent offset determined, and which may enable adetermination as to whether a reason for a lack of fuel tankdepressurization is likely due to a degraded FTPT or a degraded FTIV (ora restriction in one or more lines coupling the fuel tank toatmosphere), it is herein recognized that there may be otheropportunities for determining FTPT offset.

Specifically, it is herein recognized that a refueling event may be arare event for certain hybrid electric vehicles, such as plug-in hybridelectric vehicles, for example. Thus, it may not be desirable to relysolely on refueling events for rationalizing the FTPT and/or determiningFTPT offset. However, because a sealed fuel tank is at most times undereither positive or negative pressure with respect to atmosphericpressure, it may not be desirable to simply unseal the fuel system torationalize the FTPT, as venting the fuel tank with positive pressuretherein may undesirably load the canister with fuel vapors and asventing the fuel tank with negative pressure therein may undesirablydraw in air into the fuel tank, which may disturb partial pressures andcause further vaporization. Drawing air into the tank may alsoprematurely age the fuel therein, resulting in the fuel losing itsvolatility which is undesirable particularly in a PHEV where fuel mayremain in a tank for a prolonged period of time as the vehicle isregularly charged.

However, there are certain points during a diurnal cycle where pressurein a sealed fuel tank may be at atmospheric pressure, specificallyduring a transition from a heat gain portion of the diurnal cycle to aheat loss portion of the diurnal cycle. If the fuel system is unsealedat such a time, then neither undesirable loading of the canister nor thedrawing in of air to the fuel system may occur, and the FTPT may berationalized.

Turning now to FIG. 6, an example illustration of a diurnal cycle 600 asa graph of solar intensity and temperature as a function of the time ofday, is shown. Incoming solar radiation 602 begins increasing at sunrise604, and rises to a maximum near mid-day before declining until sunset606. As such, sunrise 604 marks a time of day near where a heat gaincycle is at its greatest, and sunset 606 marks a time of day near wherea heat loss cycle is at its greatest. Accordingly, ambient temperature608 is shown, illustrating the increase in temperature from a minimumtemperature 610 near sunrise 604, and the decrease in temperature from amaximum temperature 612 prior to sunset 606. As such, if a fuel systemis sealed during the heat gain cycle, it may be expected that pressuremay build in the sealed fuel system. Alternatively, if the fuel systemis sealed during the heat loss cycle, then it may be expected that theoutside temperatures may serve to reduce pressure in the sealed fuelsystem.

Accordingly, during the course of a diurnal cycle, there may be a pointor points at which pressure in the sealed fuel system is at atmosphericpressure. Specifically, when a positive pressure exists in the fuelsystem, as the fuel system cools during the diurnal cycle, pressure maybe reduced until the fuel system is at atmospheric pressure, just priorto transitioning to building a negative pressure in the sealed fuelsystem. Alternatively, when a negative pressure exists in the fuelsystem, as the fuel system warms during the diurnal cycle, pressure maybecome equivalent to atmospheric pressure just prior to transitioning tobuilding a positive pressure in the sealed fuel system. However,determining exactly what point at which a sealed fuel system will be atatmospheric pressure may be challenging. To accomplish such a task, awakeup circuit may be employed, which may wake a controller of thevehicle at precisely the time when pressure in the sealed fuel system isat atmospheric pressure.

Turning to FIG. 7, an example transfer function for a wakeup circuit(see FIG. 8) is depicted. Graph 700 includes pressure along thehorizontal axis (or x-axis) and volts along the vertical axis (ory-axis). Plot 705 depicts the example transfer function, which may berepresented by the following equation:Volts=0.1404*Pressure+2.5  (Eq. 1)For example, if it is desired to wake the controller in order to conductan FTPT offset determination at a point when pressure in a sealed fuelsystem is at atmospheric pressure (0), then a value of 2.5 volts may becalculated based on the transfer function (Eq. 1) above. This voltagemay be applied via a latching chip on a comparator circuit (see FIG. 8).The latching chip, in one example, may be an 8-bit latching chip. In theexample, the 2.5 volts may be programmed into a digital/analog converterwhich applies the programmed voltage on the comparator circuit.

Upon determining the zero pressure cross threshold (also referred to asatmospheric pressure) in volts, the controller may sleep while thecomparator circuit is maintained awake. The comparator circuit mayreceive power from a battery of the vehicle. In one example, thecomparator circuit may be a hot at all times (HAAT) comparator circuit.In this way, when outside temperatures due to the diurnal cycle are suchthat the sealed fuel system is at atmospheric pressure, as sensed forexample via the FTPT (e.g. 291), the controller may be woken in order toconduct a diagnostic to determine FTPT offset.

Turning now to FIG. 8, an example comparator circuit 800 operable towake the controller at a time following a vehicle-off condition wherethe sealed fuel system is at atmospheric pressure, is depicted.Comparator circuit 800 may include controller 212. The controller mayactivate the comparator circuit 800 following a vehicle-off event when arequest for FTPT offset determination is indicated. For a hybridvehicle, a vehicle-off event may include the vehicle being turned off ordeactivated completely. In some examples, vehicle-off may include akey-off event where the vehicle is powered off.

Controller 212 may include wake input 805. Wake input 805 may be coupledto one or more inputs configured to wake up the controller when thecontroller is asleep following a vehicle-off condition. In response to arequest to conduct a diagnostic to determine FTPT offset, the controllermay determine the voltage corresponding to atmospheric pressure (see thetransfer function depicted at FIG. 7). While the controller is asleep,energy may be saved by shutting down on-board sensors, actuators,auxiliary components, diagnostics, etc. Essential functions, such asclocks and controller and battery maintenance operations may bemaintained active during the sleep mode, but may be operated in areduced power mode. During the awake mode, the controller may beoperated at full power, and components regulated by the controller maybe operated as dictated by engine and vehicle operating conditions.

Wake input 805 may be configured to trigger controller 212 to wake upwhen a signal is received indicating that pressure in the sealed fuelsystem is equal to the zero pressure cross threshold. Wake input 805 maybe coupled to op-amp 815. Op-amp 815 may comprise a first input 820, asecond input 825, and an output 830. In the depicted example, firstinput 820 is depicted as a positive input and second input 825 isconfigured as a negative input. In other examples, these configurationsmay be reversed. Thus, in the depicted configuration, the output 830 ofcomparator circuit 800 may be a difference between the first input 820and the second input 825.

In this configuration, wake input 805 is configured to wake controller212 when a zero signal is received from output 830. Op-amp 815 isconfigured to output a zero signal via output 830 when the value of avoltage at first input 820 is equal to the value of a voltage at secondinput 825. First input 820 is coupled to FTPT 291. The signal from theFTPT may be processed, for example band-pass filtered, via filter 835before being communicated to op-amp 815. In one example, filter 835 maybe a low pass filter. Second input 825 is coupled to digital/analogoutput 840 from controller 212 via latching chip 845. As such, once thecontroller determines the zero pressure cross threshold, the thresholdis converted to a voltage reading (as described above with regard toFIG. 7) and the voltage reading is latched via latching chip 845. Thecontroller may sleep after the latching chip latches the voltagereading. Thus, comparator circuit 800 may compare actual pressure of thesealed fuel system as sensed by the FTPT 291 to the threshold pressure(zero pressure cross threshold), such that the controller is awoken whenpressure as monitored via the FTPT coincides with the pressurecorresponding to the latched voltage reading.

In other words, as the output 830 of comparator circuit 800 is adifference between an output of the FTPT 291 (converted to voltage) andthe latched voltage, the op-amp 815 may provide a zero signal as output830 when pressure in the sealed fuel system reaches the zero pressurecross threshold.

Comparator circuit 800 may be configured as a HAAT circuit and as such,comparator circuit 800 may be a differential op-amp circuit. Comparatorcircuit 800 may receive power from voltage source 850. Voltage source850 may be a battery or other energy storage device and may be coupledto the comparator circuit via pull-up resistor 855.

In this manner, the controller may be woken precisely at a time when itis expected that pressure in the sealed fuel system may be atatmospheric pressure. In this way, if the FTIV is commanded open, thecanister with be neither loaded with fuel vapors stemming from the fuelsystem, nor will air be inducted into the fuel tank.

It may be understood that the sensor (e.g. FTPT) for which offset isbeing determined is also the sensor that is relied upon for waking thecontroller in order to conduct the diagnostic to determine offset. Thus,if an offset is indicated, then it may be understood that the new zeropressure cross threshold may correspond to the offset pressure. Forexample, if the offset of the FTPT is determined to be 1 InH2O, thenusing the transfer function (Eq. 1) discussed above, the voltage atwhich the comparator circuit may latch may comprise 2.6404 Volts. Inthis way, the controller may be woken up in order to learn FTPT offset,even under conditions where there already is an offset determined.Comparator circuit may be used in conjunction with method 900, discussedin detail below, in order to conduct environmentally friendly FTPToffset diagnostics.

Thus, as discussed herein, a system for a hybrid vehicle may comprise afuel system that includes a fuel tank and a fuel tank pressuretransducer. The system may further comprise a fuel tank isolation valvein a conduit coupling the fuel system to a fuel vapor storage canister,the fuel vapor storage canister further coupled to atmosphere. Thesystem may further comprise a comparator circuit that includes a firstinput voltage to an operational amplifier related to pressure in thefuel system as monitored via the fuel tank pressure transducer and asecond input voltage that comprises a latched voltage corresponding toatmospheric pressure. The system may further comprise a controller withcomputer readable instruction stored on non-transitory memory that, whenexecuted during a vehicle-off condition, cause the controller to inresponse to the first input voltage equaling the second input voltage,wake the controller and command the fuel tank isolation valve to a fullyopen position. The controller may store further instructions to monitora pressure change in the fuel system in response to the commanding openthe fuel tank isolation valve. The controller may store furtherinstructions to set an offset of the fuel tank pressure transducer as afunction of the pressure change in the fuel system in response to thecommanding open the fuel tank isolation valve. The controller may storefurther instructions to adjust one or more thresholds for diagnosticroutines that rely on output from the fuel tank pressure transducer.

In such a system, the controller may store further instructions to setthe second input voltage based on a transfer function stored at thecontroller that transforms pressure to voltage.

In such a system, the controller may store further instructions to, inresponse to determining the offset, set the second input voltage as afunction of a difference between the offset and atmospheric pressure.

Turning now to FIG. 9, an example method 900 for conducting an FTPToffset diagnostic is depicted. Specifically, method 900 may be used todetermine FTPT offset, in response to a comparator circuit (e.g. 800)waking the controller (e.g. 212) to conduct the diagnostic when it isexpected that pressure in the sealed fuel system will be at or nearatmospheric pressure.

Method 900 will be described with reference to the systems describedherein and shown in FIGS. 1-2 and FIG. 8, though it should be understoodthat similar methods may be applied to other systems without departingfrom the scope of this disclosure. Method 900 may be carried out by acontroller, such as controller 212 in FIG. 2, and may be stored at thecontroller as executable instructions in non-transitory memory.Instructions for carrying out method 900 and the rest of the methodsincluded herein may be executed by the controller based on instructionsstored on a memory of the controller and in conjunction with signalsreceived from sensors of the engine system, such as the sensorsdescribed above with reference to FIGS. 1-2 and FIG. 8. The controllermay employ actuators such as FTIV (e.g. 252), etc., to alter states ofdevices in the physical world according to the method depicted below.

Method 900 begins at 905, and includes estimating and/or measuringvehicle operating conditions. Operating conditions may be estimated,measured, and/or inferred, and may include one or more vehicleconditions, such as vehicle speed, vehicle location, etc., variousengine conditions, such as engine status, engine load, engine speed, A/Fratio, manifold air pressure, etc., various fuel system conditions, suchas fuel level, fuel type, fuel temperature, etc., various evaporativeemissions system conditions, such as fuel vapor canister load, fuel tankpressure, etc., as well as various ambient conditions, such as ambienttemperature, humidity, barometric pressure, etc.

Proceeding to 910, method 900 may include indicating whether a key-offevent is indicated. In this example method, a key-off event may beunderstood to comprise a vehicle-off event, where the vehicle isdeactivated. If a key-off event is not indicated, then method 900 mayproceed to 912, where the vehicle may be operated according to driverdemand. For example, the vehicle may be propelled via the engine, motor,or some combination of the two. Method 900 may then end.

Returning to 910, in response to a key-off event being indicated, method900 may proceed to 915. At 915, method 900 may include latching the zeropressure threshold via the comparator circuit (e.g. 800). For example,if no offset of the FTPT has been previously indicated, then the zeropressure cross threshold may comprise 2.5 V, as per the transferfunction discussed above at FIG. 7. Alternatively, if there is alreadyan indication that the FTPT offset is 2 InH2O, for example, then thezero pressure cross threshold may comprise 2.7808 V, as per the transferfunction discussed above at FIG. 7.

With the zero pressure cross threshold latched via the comparatorcircuit, at 915 the controller may be put to sleep where essentialfunctions are maintained powered at a reduced level, and wherenon-essential functions are powered off. Power to the comparator circuitmay be maintained.

Proceeding to 920, method 900 may include indicating whether acontroller wakeup event is indicated. In other words, at 920, method 900determines whether the comparator circuit has triggered the waking ofthe controller (e.g. 212). If not, method 900 may proceed to 925, whereit is indicated as to whether a key-on event is indicated. For example,a vehicle operator may desire to travel via the vehicle, and thus mayenter and activate the vehicle prior to the controller being woken toconduct the diagnostic for learning FTPT offset. In some examples, akey-on event may comprise a remote start event, for example.Accordingly, if a key-on event is indicated at 925, method 900 mayproceed to 930, where the vehicle may be operated according to driverdemand, as discussed above at 912. Method 900 may then end.

Returning to 925, if a key-on event is not indicated, method 900 mayreturn to 920 where it is assessed as to whether the controller wakeevent has occurred. In response to the controller being triggered towake at 920, method 900 may proceed to 935. At 935, method 900 mayinclude commanding open the FTIV, and may further include allowing forsystem stabilization. Specifically, while the comparator circuit isdesigned for waking the controller and commanding the fuel systemunsealed at a point where pressure in the fuel system is at atmosphericpressure, depending on any inherent FTPT offset, pressure in the fuelsystem may not be precisely at atmospheric pressure. In other words,there may be some amount of pressure or vacuum in the fuel system thatgets relieved upon commanding open the FTIV.

With the fuel system commanded unsealed at 935, method 900 may proceedto 940. At 940, method 900 may include recording fuel system pressurevia the FTPT (e.g. 291). In this way, at step 945, method 900 mayinclude determining FTPT offset. For example, consider a situation wherethe comparator circuit was latched to wake the controller when pressurein the fuel system reads 0 InH2O. Accordingly, when the FTPT reads 0InH2O, the controller may be woken, and the FTIV may be commanded open.However, when coupled to atmosphere, the FTPT may read 1 InH2O, forexample. In this example, the offset of the FTPT would be determined at945 to be 1 InH2O. Other examples are possible, such as when the fuelsystem is coupled to atmosphere, pressure as monitored via the FTPT mayread −2 InH2O. In such an example, the offset of the FTPT would bedetermined at 945 to be −2 InH2O. However, while such methodology maynot enable unsealing of the fuel system at precisely a time whenpressure in the sealed fuel system is equal to atmospheric pressure, themethodology may reduce an overall amount of fuel vapors that may loadthe canister and/or may reduce induction of air into the fuel tank, ascompared to a situation where such a wakeup circuit were not utilized.For example, unsealing the fuel system when pressure in the sealed fuelsystem is 1 InH2O will load the canister much less than a case where thefuel system is unsealed when pressure in the sealed fuel system is 30InH2O or greater. Thus, by using the wakeup circuit as discussed, theunsealing of the fuel system may be conducted at times when it is likelyor expected that pressure in the sealed fuel system will be nearatmospheric pressure.

With the offset determined at 945, method 900 may proceed to 950. At950, method 900 may include commanding closed the FTIV to once againseal the fuel system from atmosphere. Proceeding to 955, method 900 mayinclude updating vehicle operating conditions. At 955, updating vehicleoperating conditions may include updating the FTPT offset at thecontroller. For example, if the FTPT offset is 1 InH2O, then such anoffset may be stored at the controller such that controller strategy mayrely on the offset value. In one example, as discussed, the offset maybe set as the zero pressure cross threshold for any subsequent timeswhere the comparator circuit (see FIG. 8) is utilized to wake thecontroller in order to determine the FTPT offset. In another example,thresholds for a presence or absence of undesired evaporative emissionstests may be adjusted as a function of the offset value. For example, ifthe offset value is 10 InH2O, and the fuel system is considered to befree from a source of undesired evaporative emissions when the pressureis at or above 9 InH2O, then if not compensated for, the fuel system maybe determined to be free from undesired evaporative emissions when infact, the fuel system includes a source of undesired evaporativeemissions. Thus, thresholds for indicating presence or absence ofundesired evaporative emissions may be adjusted as a function of thedetermined offset of the FTPT. For detailed explanation of howthresholds may be adjusted for particular diagnostics for presence orabsence of undesired evaporative emissions, refer to the description ofFIG. 3, which similarly applies to the method of FIG. 9.

In some examples, the offset may be used to compensate fuel systemdepressurization determination. For example, in response to a requestfor refueling, the refueling lock (e.g. 245) may only unlock in responseto pressure in the fuel system being within an absolute value thresholdof atmospheric pressure. Thus, an FTPT that has an inherent offset thatis outside the range of the absolute value threshold, may not enableunlocking of the refueling lock unless the refueling lock is manuallyunlocked. Thus, in some examples, the determined FTPT offset may be usedto enable access to a fuel filler neck (or in other words, unlocking ofthe refueling lock), even under conditions where the FTPT does notindicate pressure in the fuel system within the range bounded by theabsolute value thresholds of atmospheric pressure.

For example, in some cases, in response to an indication that the FTPToffset is such that the refueling lock may not open in response to fuelsystem depressurization, then the controller strategy may be updated tounlock the refueling lock in response to pressure in the fuel systembeing within a threshold (e.g. +/−5 InH2O) of the FTPT offset value. Forexample, if the FTPT offset is 10 InH2O, then control strategy mayunlock the refueling lock in response to pressure in the fuel systembeing between 5 and 15 InH2O. In another example where the FTPT offsetis such that control strategy may not unlock the refueling lock inresponse to fuel system depressurization, the controller strategy may beupdated to enable the refueling lock unlocked regardless of the pressurereading in the fuel system once coupled to atmosphere for refueling. Insome examples, control strategy may only be updated as discussed, inresponse to a predetermined threshold number of times the FTPT offsethas been determined. For example, if an FTPT offset has been indicatedthree times or more, in other words three independent diagnostics thatrely on the comparator circuit have indicated the FTPT offset, thencontrol strategy may be modified to enable the refueling lock to beopened in response to fuel system depressurization as discussed above.

Proceeding to 960, method 900 may include once again sleeping thecontroller. Method 900 may then end.

Thus, as discussed herein, a method may comprise waking a controller ofa vehicle when it is expected that a pressure in a fuel system that issealed from atmosphere is at atmospheric pressure, unsealing the fuelsystem, and indicating an offset of a pressure sensor used to monitorthe pressure in the fuel system based on a pressure change as indicatedvia the pressure sensor after the fuel system is unsealed.

In such a method, unsealing the fuel system when the pressure in thefuel system is expected to be at atmospheric pressure reduces an amountby which a fuel vapor storage canister is loaded with fuel vapors fromthe fuel system and/or reduces an amount of air inducted into the fuelsystem in response to the unsealing, as compared to unsealing the fuelsystem at a time when the pressure in the fuel system is not atatmospheric pressure.

In such a method, the offset of the pressure sensor may comprise anamount of the pressure change as indicated via the pressure sensor afterthe fuel system is unsealed.

In such a method, the offset may be used via the controller to adjustone or more thresholds for indicating a presence or an absence ofundesired evaporative emissions stemming from at least the fuel system.

In such a method, the offset may be used via the controller to adjust afuel system depressurization threshold at which the fuel system isindicated to be depressurized.

In such a method, the offset may be used via the controller to enable arefueling lock to be opened in response to a request for refueling thefuel system, without the refueling lock being manually opened.

In such a method, waking the controller may be via a comparator circuitthat relies on input from the pressure sensor used to monitor thepressure in the fuel system.

In such a method, waking the controller when it is expected that thepressure in the fuel system is at atmospheric pressure is a function ofthe indicated offset of the pressure sensor.

In such a method, in response to the controller not waking during aperiod of time where the controller is expected to have been woken,scheduling a follow-up test to determined whether the pressure sensor isstuck and is not responding to differences in fuel system pressure.

In such a method, in response to the indication of an absence of theoffset observed after a predetermined number of times that thecontroller is woken to indicate the offset, scheduling a follow-up testto determine whether the fuel system is not unsealing as expected inresponse to the waking the controller when it is expected that thepressure in the fuel system is at atmospheric pressure. In other words,the indication of an absence of an offset may be indicative of asituation where the fuel system is not unsealing, and as such, it may bedesirable to assess such a possibility. It may be understood thatscheduling the follow-up test may include ascertaining whether the fuelsystem depressurizes in response to a refueling event, as discussedabove, or if the refueling lock has to be manually unlocked in order tocommence the refueling event. In this way it may be determined as towhether the indication of the absence of the offset is real.

Another example of a method comprises waking a controller of a vehiclewhen a pressure in a fuel system that is sealed from atmosphere istransitioning from a positive pressure to a negative pressure withrespect to atmospheric pressure, or vice versa, the waking a function ofthe pressure as monitored via a fuel tank pressure transducer positionedin the fuel system; and unsealing the fuel system to couple the fuelsystem to atmosphere in order to determine an offset of the fuel tankpressure transducer.

In such a method, waking as the function of the pressure as monitoredvia the fuel tank pressure transducer may be via a comparator circuitthat wakes the controller when a first input to the comparator circuitthat comprises a first voltage corresponding to a first pressure readoutfrom the fuel tank pressure transducer is equivalent to a second inputto the comparator circuit that comprises a second latched voltage forthe comparator circuit such that a zero signal is output from thecomparator circuit. In response to the offset being determined and wherethe offset is a non-zero quantity, the method may include setting thesecond input to the comparator circuit as a function of atmosphericpressure plus the offset for subsequently waking the controller of thevehicle. The second latched voltage may be determine via a transferfunction that determines the second latched voltage as a function of thepressure when the pressure in the fuel system is transitioning from thepositive pressure to the negative pressure or vice versa.

In such a method, determining the offset may include monitoring apressure change direction and magnitude as indicated via the fuel tankpressure transducer in response to the unsealing of the fuel system, andsetting the offset as a function of the pressure change direction andmagnitude.

In such a method, the method may further comprise in response to theoffset being outside of a first threshold pressure range for indicatingthat the fuel system is depressurized, adjusting the first thresholdpressure range to a second threshold pressure range that is a functionof the offset to indicate that the fuel system is depressurized when thepressure in the fuel system is within the second threshold pressurerange.

In such a method, the method may further comprise adjusting a pressurethreshold for indicating a presence of a source of undesired evaporativeemissions stemming from the fuel system, as a function of the offset.

Turning now to FIG. 10, an example timeline 1000 is shown, depicting howa wakeup circuit such as the wakeup circuit depicted at FIG. 8 may beused to wake a controller of a vehicle at a time when pressure in asealed fuel system corresponds to a particular pressure that is latchedvia the wakeup circuit, such that a diagnostic for FTPT offset may beconducted. Timeline 1000 includes plot 1005, indicating controllerstatus, over time. The controller may be either asleep, or awake, overtime. Timeline 1000 further includes plot 1010, indicating pressure inthe fuel system as monitored via an FTPT (e.g. 291), over time. Thereare various thresholds associated with plot 1010 which will be discussedin further detail below. Timeline 1000 further includes plot 1025,indicating whether the FTIV (e.g. 252) is open or closed, over time.

At time t0, the controller is asleep (plot 1005). The comparator circuit(e.g. 800) is powered, and the zero pressure cross threshold has beendetermined and corresponds to atmospheric pressure (0 InH2O). In otherwords, with the zero pressure cross threshold determined to beatmospheric pressure, this threshold has been converted to a voltagereading, and the voltage reading is thus latched via the latching chip(e.g. 845) of the comparator circuit. Thus, in this example timeline1000, when the FTPT registers atmospheric pressure, the controller maybe woken up in order to determine FTPT offset. Thus, the zero pressurecross threshold is represented by dashed line 1011. Furthermore, at timet0, the FTIV is closed, thus the fuel system is sealed from atmosphere.

At time t1, the controller is triggered to awake mode (plot 1005), aspressure as monitored via the FTPT reaches the zero pressure crossthreshold represented by line dashed line 1011. Accordingly, with thecontroller triggered awake, at time t2 the FTIV is commanded open (plot1025), to couple the fuel system to atmosphere. Just after the FTIV iscommanded open, pressure in the fuel system rises slightly andstabilizes between time t2 and t3. The pressure that the FTPT rises torepresents the FTPT offset. Specifically, arrow 1013 points to dashedline 1012, which comprises a new zero pressure cross threshold for thecomparator circuit. In other words, because when the fuel system wascoupled to atmosphere, pressure as monitored via the FTPT rose slightlyabove atmospheric pressure, this new value representing the offsetbecomes the new or second zero pressure cross threshold for thecomparator circuit, such that subsequent FTPT offset diagnostics may beconducted using the second zero pressure cross threshold. The differencebetween atmospheric pressure and the new FTPT offset is represented by1020.

At time t3, with the FTPT offset having been determined, the FTIV iscommanded closed, and then the controller is put to sleep at time t4.Between time t4 and t5, pressure in the fuel system becomes negativewith respect to atmospheric pressure. Thus, it may be understood thatthe vehicle is in a heat loss portion of the diurnal cycle.

Between time t5 and t6, some time passes. It may be understood thatbetween time t5 and t6, the vehicle may be driven, but another FTPToffset diagnostic is not conducted. By time t6, the vehicle is returnedto sleep mode, with the pressure as represented by dashed line 1012 usedin conjunction with the transfer function discussed at FIG. 7, to latcha voltage reading corresponding to the pressure represented by dashedline 1012 via the latching chip of the comparator circuit, such that thecontroller may be woken up in response to pressure in the sealed fuelsystem reaching the pressure represented by dashed line 1012.

Between time t6 and t7, pressure in the sealed fuel system rises, thusit may be understood that the vehicle is in a heat gain portion of thediurnal cycle. At time t7, pressure in the sealed fuel system asmonitored via the FTPT reaches the second zero pressure cross threshold,represented by dashed line 1012. Accordingly, the controller is woken up(plot 1005), and at time t8, the FTIV is commanded open. Aftercommanding open the FTIV, the FTPT reading changes slightly, becomingslightly more positive than the second zero pressure cross threshold.Thus, the pressure that the FTPT registers between time t8 and t9represents a further FTPT offset. Specifically, arrow 1017 points todashed line 1016, which comprises another new or third zero pressurecross threshold for the comparator circuit. In other words, because whenthe fuel system was coupled to atmosphere at time t8, pressure asmonitored via the FTPT rose slightly higher than the second zeropressure cross threshold, this new value becomes the third zero pressurethreshold for the comparator circuit, such that subsequent FTPT offsetdiagnostics may be conducted using the third zero pressure crossthreshold. The difference between the second zero pressure crossthreshold 1012 and the third zero pressure cross threshold isrepresented by 1014. The difference between the third zero pressurecross threshold and atmospheric pressure is represented by 1015. Thus,in this example timeline, by time t9, FTPT offset has become thedifference between the third zero pressure cross threshold 1016 andatmospheric pressure (also referred to in this example timeline as thezero pressure cross threshold 1011).

At time t9, the FTIV is commanded closed (plot 1025) thus sealing thefuel system from atmosphere. At time t10, the controller is once againslept, after having latched the third zero pressure cross threshold atthe comparator circuit. Between time t10 and t11, pressure in the sealedfuel system continues to rise (plot 1010). Thus, it may be understoodthat the vehicle is in a heat gain portion of the diurnal cycle.

Returning to FIG. 9, it is herein recognized that in a situation where avehicle-off condition lasts for a duration where it is expected that thepressure in the fuel system may transition from a positive pressure to anegative pressure, or vice versa, but where the controller was not wokenup, it may be that the FTPT is stuck in range, and is not registeringfuel system pressure changes. Whether or not a wakeup is expected may bebased on knowledge of the diurnal cycle, for example the controller ofthe vehicle may communicate with one or more servers, the internet,etc., and/or may retrieve information from the onboard GPS, related tocurrent and future weather conditions, time of day, etc. In this way, itmay be determined if a wakeup of the controller is expected for avehicle-off condition.

If the controller is not awoken a predetermined number of times wherethe controller is expected to have awoken if the FTPT were functioningas desired, then control strategy may request a diagnostic such as thatdiscussed above at FIG. 3. For example, in response to a request torefuel, if the fuel system does not depressurize to enable refueling, itmay be likely that the FTPT is stuck in range. By conducting method 300depicted at FIG. 3, the source of why the fuel system is notdepressurizing (and by association, why the controller is not beingwoken up when otherwise expected to), may be determined.

Returning again to FIG. 9, it may be understood that in some examples,the controller may regularly be woken when expected to (e.g. whenvehicle-off duration is sufficient for pressure in the sealed fuelsystem to transition from positive pressure to negative pressure, orvice versa), but no offset may be indicated. While such an indicationmay be due to the FTPT actually having no offset, such a result mayalternatively be due to the FTIV not actually opening as desired and/ordue to a presence of a restriction that does not enable the fuel systemdepressurized. Thus, similar to that discussed above, if a predeterminednumber (e.g. 3) of FTPT rationalization events that rely on waking thecontroller have occurred, without an offset being indicated, thencontrol strategy may request the method of FIG. 3 be conducted. In otherwords, if no FTPT offset is being indicated because the FTIV is notopening or due to a restriction in one or more lines coupling the fuelsystem to atmosphere, then in response to a request for refueling, ifthe fuel system does not depressurize, a likely reason is that the FTIVis stuck closed and/or there are restrictions in the one or more lines.In this example, by conducting the method of FIG. 3, it may beconclusively determined as to whether there is no inherent offset of theFTPT or if the FTIV is stuck closed and/or that there are restriction(s)in the one or more lines coupling the fuel system to atmosphere.

In this way, inherent offset of an FTPT may be determined, such thatroutines that involve fuel system depressurization and/or tests forundesired evaporative emissions may be improved. For example, thresholdsfor tests for undesired evaporative emissions may be adjusted inresponse to learning FTPT offset, and in cases where FTPT offset is suchthat a refueling lock may not unlock in response to fuel systemdepressurization due to the offset, control strategy may be updated toenable the refueling lock unlocked without having to manually unlock therefueling lock. Furthermore, the systems and methods disclosed hereinmay enable a determination as to whether the FTPT is stuck in range andnot responding to pressure changes in the fuel system, and/or whetherthe FTIV which seals the fuel system is stuck closed or if there is somerestriction in one or more lines coupling the fuel system to atmospherewhich may prevent depressurization.

A technical effect is to recognize that when a refueling lock ismanually opened due to the refueling lock not being opened in responseto fuel system depressurization, when a refueling dispenser is placed ina fuel filler neck, the fuel system is coupled to atmosphere via thefuel filler neck. Accordingly, such a situation enables a determinationas to whether the FTPT degradation (e.g. offset, stuck in range) is thereason for the refueling lock not opening, or if the reason stems fromblockage in one or more lines coupling the fuel system to atmosphere(not including the fuel filler neck). Thus, a technical effect is torecognize that, responsive to the refueling lock being manually opened,such a determination as discussed above may be made based on fuel systempressure and fuel system fuel level during an ensuing refueling event.

Another technical effect is to recognize that FTPT rationalization maybe conducted at times when the sealed fuel system is expected to be atatmospheric pressure, which may thus enable rationalization withoutundesirably loading the fuel vapor storage canister with vapors, and/orwithout inducting air into the fuel system, which may disturb partialpressures, increase vaporization, and decrease volatility. Thus, atechnical effect is to recognize that a wakeup circuit that relies onthe FTPT may be utilized in order to wake a controller at precisely atime when fuel system pressure is expected to be at atmosphericpressure, in order to conduct the FTPT rationalization procedure.

The systems and methods discussed herein may enable one or more systemsand one or more methods. In one example, a method comprises waking acontroller of a vehicle when it is expected that a pressure in a fuelsystem that is sealed from atmosphere is at atmospheric pressure;unsealing the fuel system; and indicating an offset of a pressure sensorused to monitor the pressure in the fuel system based on a pressurechange as indicated via the pressure sensor after the fuel system isunsealed. In a first example of the method, the method further includeswherein unsealing the fuel system when the pressure in the fuel systemis expected to be at atmospheric pressure reduces an amount by which afuel vapor storage canister is loaded with fuel vapors from the fuelsystem and/or reduces an amount of air inducted into the fuel system inresponse to the unsealing, as compared to unsealing the fuel system at atime when the pressure in the fuel system is not at atmosphericpressure. A second example of the method optionally includes the firstexample, and further includes wherein the offset of the pressure sensoris an amount of the pressure change as indicated via the pressure sensorafter the fuel system is unsealed. A third example of the methodoptionally includes any one or more or each of the first and secondexamples, and further includes wherein the offset is used via thecontroller to adjust one or more thresholds for indicating a presence oran absence of undesired evaporative emissions stemming from at least thefuel system. A fourth example of the method optionally includes any oneor more or each of the first through third examples, and furtherincludes wherein the offset is used via the controller to adjust a fuelsystem depressurization threshold at which the fuel system is indicatedto be depressurized. A fifth example of the method optionally includesany one or more or each of the first through fourth examples, andfurther includes wherein the offset is used via the controller to enablea refueling lock to be opened in response to a request for refueling thefuel system, without the refueling lock being manually opened. A sixthexample of the method optionally includes any one or more or each of thefirst through fifth examples, and further includes wherein waking thecontroller is via a comparator circuit that relies on input from thepressure sensor used to monitor the pressure in the fuel system. Aseventh example of the method optionally includes any one or more oreach of the first through sixth examples, and further includes whereinwaking the controller when it is expected that the pressure in the fuelsystem is at atmospheric pressure is a function of the indicated offsetof the pressure sensor. An eighth example of the method optionallyincludes any one or more or each of the first through seventh examples,and further includes wherein in response to the controller not wakingduring a period of time where the controller is expected to have beenwoken, scheduling a follow-up test to determine whether the pressuresensor is stuck and is not responding to differences in fuel systempressure. A ninth example of the method optionally includes any one ormore or each of the first through eighth examples, and further includeswherein in response to the indication of an absence of the offsetobserved after a predetermined number of times that the controller iswoken to indicate the offset, scheduling a follow-up test to determinewhether the fuel system is not unsealing as expected in response to thewaking the controller when it is expected that the pressure in the fuelsystem is at atmospheric pressure.

Another example of a method comprises waking a controller of a vehiclewhen a pressure in a fuel system that is sealed from atmosphere istransitioning from a positive pressure to a negative pressure withrespect to atmospheric pressure, or vice versa, the waking a function ofthe pressure as monitored via a fuel tank pressure transducer positionedin the fuel system; and unsealing the fuel system to couple the fuelsystem to atmosphere in order to determine an offset of the fuel tankpressure transducer. In a first example of the method, the methodfurther includes wherein the waking as the function of the pressure asmonitored via the fuel tank pressure transducer is via a comparatorcircuit that wakes the controller when a first input to the comparatorcircuit that comprises a first voltage corresponding to a first pressurereadout from the fuel tank pressure transducer is equivalent to a secondinput to the comparator circuit that comprises a second latched voltagefor the comparator circuit such that a zero signal is output from thecomparator circuit. A second example of the method optionally includesthe first example, and further includes wherein in response to theoffset being determined and where the offset is a non-zero quantity,setting the second input to the comparator circuit as a function ofatmospheric pressure plus the offset for subsequently waking thecontroller of the vehicle. A third example of the method optionallyincludes any one or more or each of the first and second examples, andfurther includes wherein the second latched voltage is determined via atransfer function that determines the second latched voltage as afunction of the pressure when the pressure in the fuel system istransitioning from the positive pressure to the negative pressure orvice versa. A fourth example of the method optionally includes any oneor more or each of the first through third examples, and furtherincludes wherein determining the offset includes monitoring a pressurechange direction and magnitude as indicated via the fuel tank pressuretransducer in response to the unsealing of the fuel system, and settingthe offset as a function of the pressure change direction and magnitude.A fifth example of the method optionally includes any one or more oreach of the first through fourth examples, and further comprises inresponse to the offset being outside of a first threshold pressure rangefor indicating that the fuel system is depressurized, adjusting thefirst threshold pressure range to a second threshold pressure range thatis a function of the offset to indicate that the fuel system isdepressurized when the pressure in the fuel system is within the secondthreshold pressure range. A sixth example of the method optionallyincludes any one or more or each of the first through fifth examples,and further comprises adjusting a pressure threshold for indicating apresence of a source of undesired evaporative emissions stemming fromthe fuel system, as a function of the offset.

An example of a system for a hybrid vehicle comprises a fuel system thatincludes a fuel tank and a fuel tank pressure transducer; a fuel tankisolation valve in a conduit coupling the fuel system to a fuel vaporstorage canister, the fuel vapor storage canister further coupled toatmosphere; a comparator circuit that includes a first input voltage toan operational amplifier related to pressure in the fuel system asmonitored via the fuel tank pressure transducer and a second inputvoltage that comprises a latched voltage corresponding to atmosphericpressure; and a controller with computer readable instructions stored onnon-transitory memory that when executed during a vehicle-off condition,cause the controller to: in response to the first input voltage equalingthe second input voltage, wake the controller and command the fuel tankisolation valve to a fully open position; monitor a pressure change inthe fuel system in response to the commanding open the fuel tankisolation valve; set an offset of the fuel tank pressure transducer as afunction of the pressure change in the fuel system in response to thecommanding open the fuel tank isolation valve; and adjust one or morethresholds for diagnostic routines that rely on output from the fueltank pressure transducer. In a first example of the system, the systemfurther includes wherein the controller stores further instructions toset the second input voltage based on a transfer function stored at thecontroller that transforms pressure to voltage. A second example of thesystem optionally includes the first example, and further includeswherein the controller stores further instructions to, in response todetermining the offset, set the second input voltage as a function of adifference between the offset and atmospheric pressure.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

As used herein, the term “approximately” is construed to mean plus orminus five percent of the range unless otherwise specified.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A method comprising: waking a controller ofa vehicle responsive to a pressure in a fuel system that is sealed fromatmosphere reaching a zero pressure cross threshold, the pressure in thefuel system measured by a pressure sensor; unsealing the fuel systemupon waking the controller responsive to the pressure in the fuel systemreaching the zero pressure cross threshold; and indicating an offset ofthe pressure sensor based on a pressure change measured by the pressuresensor after the fuel system is unsealed.
 2. The method of claim 1,wherein the zero pressure cross threshold corresponds to atmosphericpressure, and unsealing the fuel system when the pressure in the fuelsystem reaches the zero pressure cross threshold reduces an amount bywhich a fuel vapor storage canister is loaded with fuel vapors from thefuel system and/or reduces an amount of air inducted into the fuelsystem in response to the unsealing, as compared to unsealing the fuelsystem at a time when the pressure in the fuel system is not at the zeropressure cross threshold.
 3. The method of claim 1, wherein the offsetof the pressure sensor is an amount of the pressure change measured bythe pressure sensor after the fuel system is unsealed.
 4. The method ofclaim 1, wherein the offset is used via the controller to adjust one ormore thresholds for indicating a presence or an absence of undesiredevaporative emissions stemming from at least the fuel system.
 5. Themethod of claim 1, wherein the offset is used via the controller toadjust a fuel system depressurization threshold at which the fuel systemis indicated to be depressurized.
 6. The method of claim 1, wherein theoffset is used via the controller to enable a refueling lock to beopened in response to a request for refueling the fuel system, withoutthe refueling lock being manually opened.
 7. The method of claim 1,wherein waking the controller is via a comparator circuit that relies oninput from the pressure sensor.
 8. The method of claim 1, wherein wakingthe controller responsive to the pressure in the fuel system that issealed from atmosphere reaching the zero pressure cross threshold is afunction of the indicated offset of the pressure sensor.
 9. The methodof claim 1, further comprising: in response to the controller not wakingduring a period of time where the controller is expected to have beenwoken, scheduling a follow-up test to determine whether the pressuresensor is stuck and is not responding to differences in fuel systempressure.
 10. The method of claim 1, further comprising: in response toindicating the offset is zero for a predetermined number of times thatthe controller is woken to indicate the offset, scheduling a follow-uptest to determine whether the fuel system is not unsealing as expectedin response to the waking the controller responsive to the pressure inthe fuel system reaching the zero pressure cross threshold.
 11. A methodcomprising: waking a controller of a vehicle responsive to a pressure ina fuel system that is sealed from atmosphere reaching a first pressurethreshold, the waking a function of the pressure as monitored via a fueltank pressure transducer positioned in the fuel system and the firstpressure threshold set as a function of an offset of the fuel tankpressure transducer and atmospheric pressure; and responsive to wakingthe controller, unsealing the fuel system to couple the fuel system toatmosphere and updating the offset of the fuel tank pressure transducer.12. The method of claim 11, wherein the waking as the function of thepressure as monitored via the fuel tank pressure transducer is via acomparator circuit that wakes the controller when a first input to thecomparator circuit that comprises a first voltage corresponding to afirst pressure readout from the fuel tank pressure transducer isequivalent to a second input to the comparator circuit that comprises asecond latched voltage for the comparator circuit such that a zerosignal is output from the comparator circuit.
 13. The method of claim12, further comprising, in response to updating the offset and where theupdated offset is a non-zero quantity, setting the second input to thecomparator circuit as a function of atmospheric pressure plus theupdated offset for subsequently waking the controller of the vehicle.14. The method of claim 12, wherein the second latched voltage isdetermined via a transfer function that determines the second latchedvoltage as a function of the pressure when the pressure in the fuelsystem is transitioning from a positive pressure to a negative pressureor vice versa.
 15. The method of claim 11, wherein updating the offsetincludes monitoring a pressure change direction and magnitude asindicated via the fuel tank pressure transducer in response to theunsealing of the fuel system, and setting the updated offset as afunction of the pressure change direction and magnitude.
 16. The methodof claim 11, further comprising: in response to the updated offset beingoutside of a first threshold pressure range for indicating that the fuelsystem is depressurized, adjusting the first threshold pressure range toa second threshold pressure range that is a function of the updatedoffset; and indicating that the fuel system is depressurized when thepressure in the fuel system is within the second threshold pressurerange.
 17. The method of claim 11, further comprising adjusting a secondpressure threshold for indicating a presence of undesired evaporativeemissions stemming from the fuel system as a function of the updatedoffset.
 18. A system for a hybrid vehicle, comprising: a fuel systemthat includes a fuel tank and a fuel tank pressure transducer; a fueltank isolation valve in a conduit coupling the fuel system to a fuelvapor storage canister, the fuel vapor storage canister further coupledto atmosphere; a comparator circuit that includes a first input voltageto an operational amplifier related to pressure in the fuel system asmonitored via the fuel tank pressure transducer and a second inputvoltage that comprises a latched voltage corresponding to atmosphericpressure; and a controller with computer readable instructions stored onnon-transitory memory that when executed during a vehicle-off condition,cause the controller to: in response to the first input voltage equalingthe second input voltage, wake the controller and command the fuel tankisolation valve to a fully open position; monitor a pressure change inthe fuel system in response to the commanding open the fuel tankisolation valve; set an offset of the fuel tank pressure transducer as afunction of the pressure change in the fuel system in response to thecommanding open the fuel tank isolation valve; and adjust one or morethresholds for diagnostic routines that rely on output from the fueltank pressure transducer.
 19. The system of claim 18, wherein thecontroller stores further instructions to set the second input voltagebased on a transfer function stored at the controller that transformspressure to voltage.
 20. The system of claim 18, wherein the controllerstores further instructions to, in response to determining the offset,set the second input voltage as a function of a difference between theoffset and the atmospheric pressure.